The round spent casting True Strike is going to seriously reduce the damage the spell gives. You're just making the spell worse. Witch Bolt isn't a good choice up to level 4, at level 5 it's worse than cantrips. Even if you stick it in a 9th level slot and do 9d12/round with it, it's still pretty much meh unless maybe you twinspell it or something. It was really dumb of them to make it take up your concentration, I can't see it getting any use for non-sorcs.
Actually, I think that the problem with the spell is the sentence that says that it no longer works if the foe gets out of range or full cover. I get the whole Emperor Palpatine vibe, but no other concentration spell in the game (TMK) stops working because the target gets out of range or jumps behind a wall.
And trust me. If you rolled as bad as I tend to do on a D20, you would True Strike it as well.
The player of our PC fighter has the same problem. He was in a fight with the half dragon from HotDQ at level 3. The Bard slept the half dragon. Another NPC came over and woke the half dragon up. The half dragon is prone, so advantage. He has advantage and misses. Then, the player decides to use his Action Surge while he still has advantage and still misses. It's so sad at times that it's funny.
At higher level when I do not mind blowing off a lower level spell slot, I'll probably stop using True Strike. But for now, my PC rarely damages foes significantly anyway so the use of the round is actually more helpful than harmful overall. In about 13 combats, my PC wizard has done about 40 points of damage with cantrips. I once did 8 and the entire table erupted. I also once did 6. The third most I've done against a foe is 4 and I usually do 1 or 2. I've never criticaled yet. Not that how I rolled in the past affects how I'll roll in the future, but I need new dice.