It's more the fact that for a few cards (pretty much only during Remilia) you have to rely on the RNG to not get completely walled. Random boss movements also make scattered cards across the game more difficult than needed, but that's more subjective on my part and nowhere near game-breaking anyway.
Really? I only get walled like 1% of the time in Remillia lunatic.
That wall only happens either in Scarlet Gensokyo (big wall on a big bubble wave) or Vampire Illusion (hard wave over near-wall).
All my other deaths were legit mistakes (ie there were obvious escape routes)
Not saying that the random boss movements don't make it very very annoying, but... it's not the walls.
Scarlet Meister is a complete BS card for me, so... didn't count that :V
Oh, and in case you don't know, Vampire Illusion "walls" are usually quite dodgable (both micro- and macrododge).
It's Scarlet Gensokyo walls that are utterly impossible, due to having 1000 other random bullets around that screw you over.
Fortunately, Scarlet Gensokyo rarely spawn that kind of walls, so it isn't that bad.
I don't think EoSD has a terrible engine at all.
I captured "Royal Flare" for the first time with someone other than MarisaA (the path through it is simpler than I thought it would be)
Your path is not bad, but it can be even simpler.
You can stay in a safespot, and the only movement you need is that down move (last move of the spell in your replay).