I've been playing a lot dtv recently and maybe there is a insane difference between NA and EU, but at least on EU side your observation doesn't quite fit to what i see.
The maps you are talking about, where i do see the problem that there could be some more room to make when the server is full, are actually the only ones where the server is full constantly and if they get changed people switch. And to make it clear, i am talking about Uzgha, Istiniar and the old sea raid from defend the village. And maybe Turin Castle, although people are already overwhelmed with 2 ways that lead bots to the visc, so usually there is barely any time to be bored.
So, and why is that those maps make the server full and the ones that are more open and allow space for every single player when there are 30 of them, empty the server? Exactly, because dtv, EU dtv to be precise, is only a handful of dedicated players that like to play for the reasons you are telling me, the rest is only there to GRIND EXP. That's why noone wants to play the more open maps, although that is the most complained about issue right after the invisible walls.
So please don't tell me that there are only those 3 groups of players, you've left out the biggest one that only play it for massive XP and Gold grind. And i didn't make the maps for those, although the small ones i mentioned up there make it seem like it. I wanted to get rid of exploiting first, bring some new ideas to dtv (the gate with winch, ballistae, ladder-assaults, bringing castles into the mode) and to make the rounds more fast-paced, so even on low population you can get at least decent xp and have some fun because bots don't take half an hour to get to you. And so far i like what is happening on EU dtv. I see way more teamplay, people form shieldwalls constantly, meatwalls and pike-walls are a thing now, too. No more "let's leech at v while 2 or 3 guys manage to kill off every single bot on the front with super nice exploits", because if you don't play along and help your team out you can cause a lot of trouble for the guys that do.
And contrary to all the QQ on the forums about the new maps and bots, i get plenty of good feedback on the servers, so i must've done something right. Not to mention that i see 2 full servers on EU side every now and then, which never happened before the update.
For the invincible shielders there will be a solution, just not sure how to do it exactly, but Shik and everyone else that has a say in this will definitely agree on one.