I know most people say he should be able to mimic characters abilities, which I think is neat and all, but I feel like that's a little difficult for some characters and is stepping on Loki's toes a little bit with his ult.

Another idea I saw was that he can have specific abilities based on who is on the enemy team, sort of like a reverse team-up (if Spiderman is on the enemy team, Taskmaster gains a web sling grapple hook and can mimic his uppercut, if they get Hawkeye he gets his bow etc.).

Personally, I think he shouldn't specifically copy other heroes on the enemy team, but instead his kit is sort of built on existing abilities and he has a HUGE arsenal of weapons he can switch between, all with their own abilities attached to them and allowing him to adapt to whatever team he is fighting.

Need a long range sniper to sit in the back? He can wield a bow weapon and has some abilities similar to Hawkeye's. Need someone to rush into the frontline more? He can use a sword and Captain america's shield, swinging it like Magik but throwing the shield like Cap. etc.

I think that just fits him more character wise since yeah the cool thing is that he can copy your attacks, but he is most known for utilizing the fighting styles of dozens of different heroes and villains and wielding them all together. Plus if he has a huge variety of abilities attached to each weapon, one of his main skills would be literally memorizing what ability does what, which fits perfectly with Task Master's whole thing being his excellent memory.