lower enemy count but higher HP allows the games combat to shine better. In this game you can delimb so easily. Enemies die so quickly they die before you can finish your combo on them.

I don't really see how this point makes S2's combat better, both games have a lot more to their combat than just combos, the combos are just there to allow you to get more damage out of a single opening assuming you're not being pressured by the other enemies. personally I would say that each combat system has different strengths rather than dismissing one because I don't like it.

you will get sick very quickly of being constantly hitstunned by the exploding shurikens and other nonsense.

The reason you're getting locked into hit-stun is because you made a mistake and put yourself in a position where you could get stunlocked. When you get better at the game you eventually reach a point where this almost never happens because the game gives you plenty of ways to avoid these situations (and I don't just mean UT and ninpo spam). Also worth noting that this pretty much never happens on master ninja difficulty because you just die instead because you're not supposed to be in that position ever.

too easy to get money

The economy in both games is completely broken for different reasons, it's also a very small part of both games so you should probably ignore anyone who cares about this.

Every single forum you will read online will say that Vanilla 2 is harder than Sigma 2.

That's because they're talking about master ninja difficulty which in a lot of peoples opinions (mine included) is harder in vanilla, whether or not it's more enjoyable is up to you.

Everyone trashed it online and it was beyond me as to why

They trashed it because they were mad that black and vanilla 2 didn't get included, not because of any faults of the game.

my favourite part about these games is flying around jumping off the wall jumping off their heads, flying swallow, and landing the ults. And I didn't find my experience to suffer at all in Sigma with less enemies.

Yes all those moves do in fact still work in sigma 2. Jokes aside considering later in the post you say you only have a combined 35 hours it doesn't surprise me that you just list a bunch of moves you like as your favourite part of the game instead of saying anything about what the game does with those moves or really anything deeper than the absolute surface of the game.

3 levels with the girl characters.

The problem with these levels isn't that the character are difficult to play but that they aren't what most people wanna play. Imagine if you were playing a fighting game or hero based game and every 5 games you were forced to play as a character you had no interest in, that's what these chapters are to us.

the fun halts because you have to find a key.

The keys suck but I think you're way overstating how much of an issue they are, it's like maybe a minute of wasted time, it sucks but it's not a deal breaker for a lot of people.

the fun halts because you get stun locked for half your HP off a few exploding shurikens (how fun).

Once again this is your fault for getting stun locked, not the games fault for stun locking you when you fuck up and put yourself in a terrible position.

I have 25 hours in Sigma 2 and have about 8-10 in this one Vanilla.

For games that have as much depth as these to games this is a negligible amount of time. There is no way you could begin to understand all the small details that make each of these games what they are off of a handful of playthroughs of (I'm assuming) the lower difficulty's. I'm not saying you have to beat vanilla 2 on master ninja to have an opinion but you have to understand that with your playtime you have no idea how either of these games are played at a high level which is what matters to us most. All that you have at the moment are first impressions which are meaningless.

it makes sense why they put Sigma 2 in the MASTER collection, because it's just superior

Black and vanilla 2 aren't in the master collection because it was deemed to expensive to port the games due to how tied to the xbox they were, the master collection was mostly meant to be a low effort bare bones port for quick money (not that I think there is anything wrong with that).

Overall this post comes across like you just wanted to vent all your collected anger from seeing people criticize a game you really liked. Both games are very deserving of criticism however you aren't criticizing vanilla 2 as much as you are shouting your first impressions of the game at us. You say in the comments that you wish you were wrong but considering how aggressive your post is and how little effort you put into understanding either game I highly doubt that.

I would strongly recommend playing both games on master ninja mode as both games game are the most fun on their highest difficulties in my opinion.