You don't need vehicles the reasone being the tau are your fire support and thaw what ba vehicles so you have tau to do it for you and you are in charge of
cc.
The
pf can kill a dread much easier because you are not hitting on 6s also for
cc you squish a guy or 2 in combat.
Also for charging tanks you will be
str 9 so most things having armor 10 at rear means bye bye tanks.
If you run mephi up one side of the board with a lib casting shield he gets a 5 up cover save.
The only ones that spam plasma or melta are
IG so if they shoot him then you assault marines will rip them to shreds and against las he has a 2 up 4 up making him even harder to kill.
This way if you run into the big units or tough units you can do serious damage wig Mephis 7 attacks on the charge and the lib and assault squad striking befor you get hit back usually mephi kills 5 atleast usually 6 to 7 and the libs attacks that ignore armor re rolling to hit killing 2 to 3 plus the 20 plus attacks from the squad re rolling 4s usually and wounding on 3s on the charge can kill a whole lot befoe they get attacked back so that way finish them off in your opponents assault phase and move on in your turn.
Mephis squad will clear off infantry really fast like I mean for me he killed vulkan and friends in 1 turn ( 1500 points doubles)
punched out a dread right after then shot clagars last body guard in the face and did 3 or 4 wounds to calgar and he was finished off by an assault marine

so him with an assault squad is extremly powerful and Killy hope I made some sense and made my point