C2 biggest and strongest points are it's Event Sheet system. So I will explain why GMS seems more stable on performance than C2.
It's Event Sheet are great to program with. They are super easy to code with. They are a clever way of bridging Visual Programming with Coding. I firmly believe that C2 EventSheet design could and should be a standard for game development. In fact I believe in a few years C2 could end up being the Unity of JS based game development.
However, the big weakest point of EventSheets are the fact that they are designed as GAMELOOP code rather than Object based code. This is important to note because I worked with GMS and GMS is an Object Orientated game design. Most code you do in GMS is part of an object. I do believe GMS does have LOOP code, but most of your work is done in the object's own code.
This results that GMS know can package and be more efficient with Object based coding. Where as all EventSheet codes will be in the main game loop. With the us the developers in no way being able to get our ES code into the object there is no way to exclude the size of the main game loop. So even if there is an Event even if you want it unused will still be in the main game loop. So do to this performance is a lot harder to manage in C2 than any other OO design code.
Now some of us requested that Objects such as an Plugin instance can have there own EventSheet; so that the code won't be added to the gameloop. But the idea was considered not worth it. I suppose the problem leads that small games don't suffer this problem infact it's near impossible. But as the more robust a game get's and more importantly the interconnected features a game may use the speed cost becomes much larger.
As an example in my Point & Click adventure game The Blue Code. Even though nothing might be happening the CPU cost is always a minimum of 20%. The reason is because TBC has many many small features to achieve what the game manages. Even parts that don't do anything most of the time ended up carrying a cost.
Is there way around this. yes, but this requires A LOT more diligence in code design than GMS does. This is why there are so many threads happening these days. because as more and more people join the community they are starting to exemplify an underlying problem. C2 is more work to optimize.
I also agree about the exporter. I think the native language should have been JAVA. Java has fantastic conversion tools to other languages. even if C2 was built for Java to JS it would be better off. But that's purely opinion.
Just as a sample. I created a capx with nothing but 1000 GROUPS. No events. Just groups. This is not practicle no one is going to have just groups. But this is a sample of what I'm talking about.
Just groups uses 27.6% on my computer. Doesn't sound like alot. It isn't, but theres no math. it's just a code group.
As it is I'm not sure how we are going to managed our game The Blue Code without a re-write