The "third-party problem" is a fascinating one in Apex, something I've thought about deeply over the game's lifetime. The Support changes and prevalence of red armor were a very deliberate attempt to increase survivability and boost multiple Legends with abilities that help you reset, or simply have a moment to process what to do for your next move. But that also made fights more drawn out, increasing the risk for third-parties. But maybe because fights conclude sooner now, players have more time outside of combat and are more frequently looking to third-party? Looking at some dashboards, there doesn't appear to be any notable shift in "dead time" between this season and last, but lobbies are expectedly dying slightly faster than last season. Why do you think there have been more third-parties? Shouldn't there be less, if fights are concluding faster? Could it be the map rotation? These are some of the questions we ask ourselves when trying to understand player experience and motivation.
As someone climbing through Diamond ranks right now, I would challenge the assumption that there have been "a lot more third parties." I sense a slight uptick, possibly because players feel more empowered to seek fights with an aggressive Legend meta and higher success rate converting damage into kills. This is compounded by the map rotation. But I also think the distinct lack of survival focused Legends makes us feel more powerless when things turn south, compared to last season. When the third-party came last season, you dropped Gibby bubble/Newcastle walls/Lifeline halo (or your Loba solo-queue third has already teleported to the crafter two POIs over). Reset potential gave good players more agency to react, whereas now there's more of an emphasis on rewarding preparation and strong positioning before a fight starts unfolding. I think "managing the third party" is a necessary skill to master in higher Ranks, and I think players at all skill bands are adjusting to the radical shift in "combat feel" between this season and last.
Personally, I think Ranked is not punishing enough for poor placement. As long as that's the case, regardless of meta, you will have players that are motivated by KP more than strategizing for end game. Unfortunately this isn't a Ranked AMA and I'm not a Ranked designer, but I do provide my input from a dev and Ranked player perspective. It's all I play, and I hear your concerns about ladder progression.
On your last point, on the impassable wall ability. I've thought about that exact same thing but I think the devil is in the details... how big is it... Seer ult size? A whole POI? Wouldn't that attract more players to the area? Can other players see it? Is audio muted inside of it? Can enemies leave it? Is it an ult? What other "stuff" should it do to feel ult-like? Make your pitch!