The problem is not tac marine in generall, the problem are 1-2 doktrins on them!
I don't know if you follow the 1vs1 since last patch, but there is a "new" meta build out for spacemarine!
The real problem is in my opinion shoot while moving.
Okay short description to this build.
They play with killteam, diomedes,and terminator(7 point melee elite)
Doktrin's, shoot while moving, tireless, imporved LP!
And then, spam Tac marines -> infantrie upgrades, later on upgrade some tacs to plasma tacs!
Thats basicly the full strategie!
i wrote this allready before the patch hit , the powernerf is not a good idea in generall, and for nerfing orks, you should find a better way!
Now we have a really monoton metagame.
Espacialy shoot while moving is against eldar completly broken! and atleast on 3 from 4 maps, you get the map control just cause of tireless+shoot while moving+ forward barracks. Eldar can't do anythink against this.
Ah and if you play against eldar, take instead of killteam gabriel, and rush to diomedes.
Killteam is in generall really bad against eldar, (cause scoprion)
So open up with triple tac, go for mapvision with barracks, and stay 2 min back without a elite is way better, then summoning killteam.
With diomedes on min 6, Eldar is pretty much fucked, falcon cannot come so early, and all other unit's cannot trade against diomedes + tacs .
So yeah , you force the Eldarplayer to play from 1 point out, while you got full map control
If you don't believe me, watch some streams or just play 1vs1 for your self.
The top sm player atm, (they who still play) play all the same strategie.
Babyubyu , 2 other kor player, then 1-2 other players under top 10 , but i cannot remember the name.
All of this use exactly the same doktrin and strategie.
Thats what we get, if we nerf our ressource system so badly, and also doesn't open up more strategies for us.
Now you are forced to play t1 units + upgrades until min 10 ! only ork can commit to a early truck, but In generall, all 3 races has to push t1!
Very good for forward barracks, on 3 from 4 maps.
Well designed boys.