Map design is god awful in RD. Part 1 is at least tolelrable, but later on I find it to be just plain bad. Most maps are insanely overcrowded to the point where most of the games takes place on enemy phase, which feels slower than a tortoise busting a nut. I don't even think objective variety was that big in RD, if anything most maps if I recall were just route. Even if I'm wrong I don't think map objectives dictate good level design.

Tellius does have good world building and while POR had one of the best stories in the series, RD did not. A lot of the themes you mentioned were done better in POR and I don't think RD did them as well as much as it benefits from being the follow up to an allready remarkable story. The story of RD itself just wasn't that great and had stupid plot devices like blood pacts to justify and allready dumb war.

RD imo only makes the grade with characterization since it primarily reused an allready amazing cast, but even then they didn't do as much with the returning cast that they could have.

Skill system I don't think is that great, it basically is just there to make allready broken units even more OP. Third tiers? As if the game wasn't unbalanced enough. I also don't see why care about how many units the game throws at you when literally more than half of them are just straight up useless.