I call all souls style games by FromSoft "3D Igavanias" because that is what they are to me. They do not have platforming on the level of Symphony of the Night but by and large the gameplay challenge and collection loop is similar. Some people think Smash Bros. is a fighting game. Just don't expect these genre tags to make any sense.
well, Metroidvanias' (Igavanias') main gimmick is the obtaining of new items that give you abilities, which then let you enter new paths of a map by using the ability. like the ability to jump higher, or to fly, or to break objects etc.
this is then used as puzzle elements across the map, where you have to think about where to use which new abilities in order to progress further.
Which is something that doesn't happen in FromSoft's Souls games btw.
I don't think genres are hard to define at all. pretty straightforward.
you see what differentiates one genre from another and draw the line.
Souls games without the soul loss/retrieval system are just action RPGs.
because many games before them had basically all the elements that Souls games have, except the soul loss/retrieval mechanic.
Having set respawn points, respawning enemies, RPG elements etc. was done before, and was done in similar ways to Souls games.
they came onto the scene with this new mechanic and defined a new genre.
the difficulty of the games, as well as the set checkpoints instead of automated respawn points were simply a vessel to make the soul loss/retrieval mechanic impactful, since a game that's too easy would make this mechanic trivial.
but knowing that you'll be reset all the way back to the last bonfire, and have to work your way back to your current location is what builds the tension in them.
Metroidvanias without abilities that let you enter new parts of the map are just... Action Adventures.
Igavanias specifically without new abilities unlocking more of the map would just be Action platformers with heavy RPG elements.
WuKong specifically is just a hack n slay akin to Ninja Gaiden, with slightly slower and simpler combat... it has skill trees but no real RPG elements, it has no soul retrieving, not even really interconnected levels like FromSoft souls games. it's a very straightforward hack n slay that happens to have combat that is slightly toned down.
Remnant is simply a coop Shooter with heavy RPG elements. a genre mix basically. but it has almost nothing in common with FromSoftware's souls games other than elements that every game with heavy RPG elements has in common with them.
it doesn't even really have the same feel to it. you do not need to carefully proceed through nee environments due to every enemy being possibly deady, or due to traps and suprise enemy attacks possibly waiting behind every corner, like it is often the case in Souls games.
in Remnant you just run and gun through levels with your friends and mow down often dozens of enemies at once while flinging around weapon abilities here and there.
it's extremely comparable to Diablo in that way, with the biggest difference being the loot system, which is randomised like in Diablo, but with set weapon stats instead of random ones.
I truly feel that if you removed the Shard checkpoints with simple teleport icons on the map, it would still functionally be the same game, but noone would make the connection to Souls games.
it's a very superficial connection, as systems like the Shards are just like coffins in Symphony of the Night or Save Stations in Metroid... they fill you back up and respawn you... that's not a Souls thing, that's a Metroid thing lol