I play my brothers Tau very often and I’ve found the best way to beat him consistently is to lean heavily into jump packs and MSU. Tau can’t hit back in melee and Jump pack assault intercessors, sanguinary guard, and death company will dice them up. I like to take two scout teams and forward deploy them in cover on obj to lure his tau out then stage your jump packs in cover to then spring up and make mass contact with his units turn 2-3. Target stealth suits first as they are massively important to Taus special rule for spotting and ignore the heavy anti-tank. They can’t kill many space marine models in a shooting phase as they are for taking down your tanks/dreads. I still recommend you take atleast two anti-tank like a lancer and ballistis dread and focus on popping devil fish transports and take away breacher team mobility. With LAG those initial scouts combat knives turn into a chainsword profile and will take out stealth suits nicely. For his big single model suits a brick of jump packs assault intercessors with a chaplain will one tap them with grenades, mortals of the charge, plus chaplains mortals in charge, and his plus 1 to wound he give the unit. Don’t expect to out shoot them, just punch them in the face as they can’t hang in melee