I feel it's a definitive ending because I feel like it says all they wanted at that point while also offering a conclusion to the surface plot.
I know people like to rag on the show because anime fans in thier teens probably use to proclaim the show was deep and "smart". No the show may not be the most incredibly written show ever and it's psychological stuff can maybe be amtuer at best. But I feel that is such a narrow minded version of criticism, this "does the writing hit this level or not". The show is very rough around the edges and in that it honestly feels like a very honest expression of brokenness and issues that people who have a hard time self-identifying or relating to the others feel. And in a way I do feel the show is pretty well done with some pretty well developed characters and storylines they find themselves in.
Saying all that, what I'm trying to get it as to me Evangelion is about people trying to connect and live and so while the tv show offer's an ending thats fine, I also think the movie does the same. I dont actually think it's that vauge and really concludes what I think the show is about. Shinji make's peace with himself and realizes that that world that SELLE wanted, where you can't be hurt because everyone is one being is wrong. Running away from others is wrong and while life is painful, life can be great. It can be great anywhere, you just have to self-realize and be at peace with it and yourself. And this all happens plot wise. He's tempted with the choice, realizes it's wrong, and then rejects Third Impact. Comes back to a shitty world, but maybe it can work. We don't know for sure, but that seems to be the point.
So for me EoE concludes all the themes the show was trying to say. And it concludes the plot stuff too. People give Evangelion shit or look too deeply into the Biblical stuff. It's pretty clear now to a fan of Japanese stuff that the bible stuff is just a style for the robot show. Like how sentai shows have different styles and themes for thier seasons.Or how jrpgs borrow from Norse or whatever else mythology. They just went all in with the Christian Imagery. Lot of that stuff is just a vehicle for whatever the writers wanted to explore. Which is what Third Impact was. It's not really important to me how you get to Third Impact, but more so what it's about. Which is basically yeah the human condition. Self vs others and whatnot. Would it be better if we all did'nt exist and where one being so we wouldn't hurt each other. You see Shinji's life and maybe it would be. So in EoE you really get to see all of what Evangelion was leading to. And it's a great ending to this really rough and rumble show.
You can argue if the tv show meets the same conclusion or not. If completion happens or doesn't. I don't know. I think last time I watched it, I thought it basically was the same ending. It's just clear that they did'nt have the the time or money to show the character and plot stuff. So they just went with the character stuff. I like EoE, because I feel you get both.