Once you end EV's story and the Heart stories, you're done with the game. Multiplayer exists true, but is horribly balanced, the puru puru finishers gets old pretty fast.
Once you end SK2's story and the youma mode, you're done with the game. And there is no other multiplayer available to keep things going.
And how isn't EV repetitve? Every single level is
beat mooks->beat boss->repeat
It's not that it isn't also repetitive (it's a beat-em-up...that's a given); I mean that SK2 has far less stages available, they are smaller, and you often engage in the same fights with the same few enemies again and again. It's very repetitive, even for the genre. EV has more variety outside of the beginning of the story mode (which has you playing on that beach level far too many times).
SK2 in contrast has the youma den and the extra missions with different goals to keep things fresh, every character has a pretty complex gameplay and is diverse enough to keep the player interested.
The youma den is just more of the same fights, on the same single stage, against the same enemies. You're right in that the characters feel more diverse and those extra abilities are nice, but the huge amount of characters and their different play styles in the Versus games is also quite welcome. You keep mentioning "extra missions" but still haven't explained what you're talking about yet. Do you mean the DLC? Because it is largely a disappointment and also more of the same outside the shooter levels.
SK2 tried different things with it's DLC while EV's just more of the same.
Unfair to say this when EV isn't done with its post-game content yet. They just announced a new 4P co-op online survival mode for patch 1.11, which is up today, for example.
SK2 had three sets of DLC that added some chibi character models (highly limited in movesets), the shooter stages (cool, but very light on content), and...a boob size slider. It's not really a lot of stuff that extends the life of the game.
Have you played Estival Versus yet? It's weird to me that you are so opposed to the game. I don't see why anyone who likes Senran Kagura would not want to play it.