EDIT: Had a bit of a brain-fart moment and somehow didn't realise there was more than one page to this discussion, so this response is probably somewhat out-of-place depending how the last 12 pages of discussion have gone.
Yes, there can be performance issues with the software, but the larger part of your complaint seems to be about poor communication from Scirra, and personally that's been the opposite of my experience.
See for example their tutorial on "Physics in Construct 2 : The Basics", which states:
[quote:z0stt7ae]Physics simulations are very CPU intensive. It can take a lot of processing to work out the proper motion. To make sure your game runs fast, it's recommended that you don't use too many objects at once. Over 100 physics objects moving at once is likely to slow your game down. Also, phones and tablets have much more limited processing power than a desktop computer. If you're targeting mobiles, you should be very conservative, and try not to have more than 20-30 physics objects.
Their "Performance Tips":
[quote:z0stt7ae]You must test on mobile from the start. Since your computer may be well over ten times faster than your mobile device, you may inadvertently design a game that has no hope of running well on a mobile device and not find out until later. To avoid surprises test regularly on the intended device to make sure it is still running fast enough. The Preview on LAN feature can make this quick and easy. You should aim to design simpler games for mobile devices to match their lower speed and resources.
...and...
[quote:z0stt7ae]Too many objects using Physics
The Physics behavior is very CPU intensive. Using too many objects with the Physics behavior can cause considerable slowdown. You should design your games to use a few large Physics objects rather than many small Physics objects.
The "Best Practices" article says:
[quote:z0stt7ae]Perhaps the most important is when developing for mobile, test on the target mobile device from the start. Your computer could be 10 or 20 times faster than your mobile device, and something which runs fast on your computer may be unplayably slow on the mobile device.
The blog entry "Optimisation: don't waste your time" says:
[quote:z0stt7ae]Realistic physics simulations are extremely processor-intensive and having over 50 physics objects can reduce the framerate, especially on mobile. Simply using fewer objects usually fixes this.
To me it seems like they've tried to be pretty clear: performance on mobile is not as good as in the browser, physics should be kept to a minimum, you'll need to design simpler games, etc. If you read and follow that advice, and are willing to put some effort into following all of the other advice given it's possible for simpler games to perform very well even on mobile.