Tony Vargas
Legend
Fighters are being shoe-horned into a role: the role of "guy who fights exactly as hard in ever round of every day until he's dropped." More seriously, the no-daily-resource-management or 'consistent performer' role. Not that there are roles in 5e, anyway.I do not like marking and I don't want fighters to be shoe horned into a role.
As for some use of CS to support the Defender speciality, I think it's a fine idea. It could be part of a Shield-based Fighting Style that merely synergizes well with Defender, or it could be an option available to Fighter-Defenders.
Even if the fighter were given a defender-useful CS option out the gate, nothing would force anyone to actually /use/ it, using CS dice for damage all the time would still be a perfectly viable option.
And, really, that's the 'worst' case.