Ashley, I agree, it is not Construct's fault. Maybe the issue here is why Construct is advertised as capable of making games playable on any mobile. Am sure in the future mobiles will be capable of a good performance on html5, but right now they clearly are not, for intense graphics as demanded by a game. I would add your comment above to the marketing schema, underlining that only "extremely simple" games perform well on mobiles.
In the meantime, I did a couple of builds on phonegap. These are done with licensed Construct2 R72, and the builds are for BB, android, webOS and symbian. (These are signed by phoneGap, and am not willing to put my iOS signing keys on line!).
I modified the ize catapult example to see how physics perform on the device. On my BB torch, it runs as a turtle. I placed no time diff to see how slow it can look. It is fluid, but slow, on both builds, with or without webGl. I am preparing a test without physics, but in the meantime you all can install and test this builds.
Here are the public pages with barcode and OTA links.