With Ares, once they block one GP they have to make a read to re-establish their zoning game or get in. When I played 1man3letters' Ares it seemed hard for him to establish his own zoning game because of Nightwing's plus frames.
With Lex, Nightwing can keep hassling him to prevent him from getting his trait out with Ground Pound. I used to play @
DreadKnight1's Lex regularly and it seemed overall easier for Nightwing to do his thing than for Lex to do his. Lex gets outzoned with Ground Pound and it's super easy to trip guard him because of his slow-ass jump arc. He gets bodied on wakeup because once you establish the threat of MB B/F3 and baiting the wakeup they'll soon stop. If he catches you with trait on KD though that's when the MU starts to shift to Lex's favour. The whole 'Whoever gets momentum first wins" statement is certainly true, although it's just slightly harder for Lex to get some momentum going than for Nightwing imo.
You're completely right about Joker, but he has to get in before he can establish his game which is the only thing that's saving me from eating my words lol. Also, his J3 is really good but his J2 is fairly easy to anti-air in staff. Joker's wakeups aren't the best so once you knock him down you can go for some oki setups