I don't know about Kongregate but since this topic is more about the Mobile IAP.
First, I actually agree with you all that Scirra should hire developers to make C2 third party plugins.
But still, regarding the Mobile IAP, there is no problem monetizing. I have tested them all and they are fine!
You see, you are over-complicating things. Scirra is actually designed like this and we can't do anything about it, you can wait for C3 (but I have a feeling it won't make any difference with the plugins) , buy an expensive program with complete features or use free Unity also with full features but you need to code, it's just like making C2 plugins in the first place.
If you need 100% free admob plugin:
If you need a free admob plugin that has reward video interstitials... The only downside is that 2% of profit goes to the developer but you can just buy it for $20.00 for all earnings to be yours:
If you need an IAP that is 100% working (Paid) : its only $10.00 or you can email cranberrygame for a discount if it's too much for you. The pack include 90+ usable plugins that will suite yor needs in mobile development.
Now that you have the links. You can now monetize properly. I don't think the program / team itself is the problem. If you have been reading around the forums & using google as it was intended, then you wouldn't have any problem in the first place. Instead of complaining, find a way!
And we all know why we use C2, it's because it's 'cheap' and easy to use. If you want free & full-packed features then there is UNITY 2D but you need to work harder to learn to code. Or you if you are rich, buy buildbox!
PixelPower - The people you mentioned that left C2 , they have left because C2 is purposely intended for starting game developers. Once you earned money and bought the Business LIcense, you then need to find a better program to suite your bigger needs. That's why I am here.
Just in case you don't know, Buildbox forums is deserted.
Artpunk - I don't know what's happening with PC or Browser exports, so I feel sorry for your situation right now. That sucks.