Well, but you said you wouldn't let the TWF PM idea work due to your death stare
So you're OK with it working for monk, what about barbarian berserker frenzy?
And the TB/SM build using his shield as a TWF weapon and still getting his free shove?
I guess the point is: are you playing that it is cool to just combine the TWF attack with whatever other bonus action attacks you can come up with? Or are you really restricting the bonus action to non-attacking things like cunning action etc.
Because if you just let TWF stack up then I think some of the highest DPR characters in the game will get better.
Actually it was my scorn stare, and it isn't that effective.

As for frenzy, sure. How many resources is being dumped into it? With no level dips or feats it is 1d6+Str+2 twice and and extra 1d6+2 for the off-hand attack. That is still less than a two handed sword that does 2d6+Str+2 twice. If he takes a level of Fighter and the Dual Wielder feat it is 3d8+3+2 x3, but he is giving up stuff to get it.
I honestly don't know what the TB/SM build is. I get Shield Master? But how do you Two Weapon Fight with a shield in your hands? I guess that has something to do with the TB part?
Really I haven't seen anywhere where the increased damage from stacking Two Weapon Fighting with something else isn't still out damaged by some other combination that is already in the game. Or if it is, you are giving up other things in order to do just a few points of damage more.