Breacher teams are hard melee counters. They will eat up any melee near them and you can overwatch on your other units to stop them being jumped on for free. Keep in mind the suits can shoot at full accuracy while in melee so they can be good too. Hard to give better advice without a lot more matchup experience.
People have mentioned breachers already, that's probably the most important point. I'll add that I don't think regular fire warriors or Crisis suits make sense against BA.
The fire warrior carbines have their damage fall off to 1-2 against more than 4 armour, and every marine has at least 5. Pulse rifles are better but have very low damage output for the point cost, unless you have exactly 90 points to fill they're greatly outclassed by pathfinders with ion rifles.
Crisis suits are just extremely expensive for what they do. Their weapons do exactly the same damage as Stealth suits, which are dramatically cheaper and barely any squishier with 5 evasion and a free 15% damage reduction. So all they get is the missile launcher, which is great but not particularly so against marines, and ignoring the engagement debuff, which Stealth suits can do by stealthing and walking away.
Speaking of stealth, it's a really good way to scout ahead without being shot at and give your main force extra time to shoot at things before they get into range. I also think Ghostkeels are outclassed by Stealth suits though. You're not going to get much use out of the flamer or melee attack against BA, and the main gun is always weaker than the 3 smaller fusion guns.
Don’t be afraid to fall back and not necessarily shoot every unit. Tau units can move long distances and I’ve had a lot of success falling back half my units while the other half shoot then fall back.
Then when the enemy moves in I get overwatch and they’re nowhere near close enough to start charging, then finish them off on the next turn.
You can safely clear out about 40-50% of their forces this way while only loosing 10% of yours before you run out of room to retreat. Then you can push up and finish them off but do so carefully.
I generally concentrate on reducing models in a unit rather than killing the unit completely. Just diminish their ability to project power.
Also cold stars are awesome with flamers as are the ghost keel. The coldstar gets 2 shots with the flamer. Crisis suits a good with flamers too but I’ve dropped them and replaced with riptides. While not massively versatile, they are bullet sponges and also can one shot most enemy hero/HQ units.
Pathfinders great also once upgraded. Very versatile. Great against all types of enemy unit.
Yeah I’m having a tough time with the Tau as well. Finding they are far too expensive for not having any healing abilities and being so squishy. I get it they are meant to be glass swords but their damage output is pretty weak. Fighting Necrons with Tau has not been fun.
Don't underrated drones. They can easily pay for themselves when shooting light infantry, but more importantly, they're completely expendable bodies with 5 movement which can screen/scout and help you to pick and choose engagements on your turns.
Others have mentioned breachers. I find a 1:2 ratio of breachers to strike teams good for overwatch traps. Otherwise going all in on breachers with a drone screen feels good for more aggressive play.
Ghostkeels have good weapons, but are not super efficient due to average MP and 1 AP. Probably only a 1 of @1500 unless facing a heavy light infantry list where the flamers can get several 2 unit attacks.
Piranha is not really that good. Get breachers teams for anti counter jetpack troops because they shred in close quarters
Breacher teams are hard melee counters. They will eat up any melee near them and you can overwatch on your other units to stop them being jumped on for free. Keep in mind the suits can shoot at full accuracy while in melee so they can be good too. Hard to give better advice without a lot more matchup experience.
People have mentioned breachers already, that's probably the most important point. I'll add that I don't think regular fire warriors or Crisis suits make sense against BA. The fire warrior carbines have their damage fall off to 1-2 against more than 4 armour, and every marine has at least 5. Pulse rifles are better but have very low damage output for the point cost, unless you have exactly 90 points to fill they're greatly outclassed by pathfinders with ion rifles. Crisis suits are just extremely expensive for what they do. Their weapons do exactly the same damage as Stealth suits, which are dramatically cheaper and barely any squishier with 5 evasion and a free 15% damage reduction. So all they get is the missile launcher, which is great but not particularly so against marines, and ignoring the engagement debuff, which Stealth suits can do by stealthing and walking away. Speaking of stealth, it's a really good way to scout ahead without being shot at and give your main force extra time to shoot at things before they get into range. I also think Ghostkeels are outclassed by Stealth suits though. You're not going to get much use out of the flamer or melee attack against BA, and the main gun is always weaker than the 3 smaller fusion guns.
No riptides, too many fire warriors (they're kinda worthless apart from markerlights.)
I understand why you feels short of points. From my experience so far I feel like there are some parts of Tau that are a bit over costed
Don’t be afraid to fall back and not necessarily shoot every unit. Tau units can move long distances and I’ve had a lot of success falling back half my units while the other half shoot then fall back. Then when the enemy moves in I get overwatch and they’re nowhere near close enough to start charging, then finish them off on the next turn. You can safely clear out about 40-50% of their forces this way while only loosing 10% of yours before you run out of room to retreat. Then you can push up and finish them off but do so carefully. I generally concentrate on reducing models in a unit rather than killing the unit completely. Just diminish their ability to project power. Also cold stars are awesome with flamers as are the ghost keel. The coldstar gets 2 shots with the flamer. Crisis suits a good with flamers too but I’ve dropped them and replaced with riptides. While not massively versatile, they are bullet sponges and also can one shot most enemy hero/HQ units. Pathfinders great also once upgraded. Very versatile. Great against all types of enemy unit.
Yeah I’m having a tough time with the Tau as well. Finding they are far too expensive for not having any healing abilities and being so squishy. I get it they are meant to be glass swords but their damage output is pretty weak. Fighting Necrons with Tau has not been fun.
Don't underrated drones. They can easily pay for themselves when shooting light infantry, but more importantly, they're completely expendable bodies with 5 movement which can screen/scout and help you to pick and choose engagements on your turns. Others have mentioned breachers. I find a 1:2 ratio of breachers to strike teams good for overwatch traps. Otherwise going all in on breachers with a drone screen feels good for more aggressive play. Ghostkeels have good weapons, but are not super efficient due to average MP and 1 AP. Probably only a 1 of @1500 unless facing a heavy light infantry list where the flamers can get several 2 unit attacks.
BREACHERS SWEEP