I know details of combat powers haven't been discussed much, and it may already be designed in a way that it isn't even an issue. I thought this might be something to mention before it gets too far along just in case since many games leave longstanding issues in place from launch throughout the entirety of the game's lifespan.
I've seen that there are a few power previews of summoned walls/obstructions to block enemies. I recall several abilities in ToG that were almost never used in a team setting (or ever in some cases) for being more of a hindrance than helpful and I'm wondering how visually or physically obstructive these summoned objects are to allied players and if they'll immediately become a nuisance.
ToG didn't have summoned stationary objects that I can think of at the moment, but some of the more taboo abilities they had when it came to team play are ones like Dimension Shift, Black Hole and Detention Field (making enemies intangible and unaffected by attacks), Phantom Army (Invulnerable summons that generate a lot of aggro and run all over the place, messing with tank aggro control and spreading enemies out), or really any aoe knockback ability (spreading enemies out).
In Warframe, one of the playable frames, Atlas, has a summoned wall to block enemies. Fortunately, allies can walk through it completely unimpeded but I had seen several complaints over the many years I played that about it visually blocking players' line of sight in certain maps. Though, that is a shooter so it doesn't use lock-on targeting for attacks like a traditional mmo, but I wanted to make sure visual and physical targeting won't be an issue with these obstructions as well as our physical movement.
"My name is Ozymandias, King of Kings: Look on my Works, ye Mighty, and despair!"