I have read this common myth here and other forums for a while now.
Its common sense in some topics here and other similar software communities that HTML5 is not ready, here in particular with Construct2 performance is attacked and this may be related to how JavaScript performs as well HTML5 with allot of elements/layers.
Some even suggest to go with Unity completely, but from my background experience which comes completely from a non game world there is always something missing in such debates. So far web development has never once go back, but always forwards into the future.
Even the Facebook owner said betting on HTML5 was a mistake. Another company that focused on HTML5 Moblyng shuts down.
But personally I think all of this debates are just plain silly. Its just not the time for heavy gaming in HTML5 today, but it will be. There is no going back and there is nothing you can do, it will be the future, regardless if its html5 or html6, or html7.
The biggest attack is always mobile and how ugly performance is, but most mobile phones released today are just or more powerful than small computers, so there is absolutely no way mobile phones will not improve performance, it has to do in particular with browsers running in mobile phones, which are improving and so will HTML5 games.
Its possible and it will be possible to create great HTML5 games in the future, this includes with Construct2 as they are limited to only what HTML and JavaScript can do. This is a tool that makes it easy for non coders to develop, but it still has to rely on external libraries, and once this improves, browsers improve, and computers improve, so will your games done with Construct2 or any other html5 game engine.
Look what this guys from Facebook and Google are doing.
It looks they will release this for developers as well in order to develop your own HTML5 games. This is the biggest prove that HTML5 can perform well and look great as well run in a browser natively:
http://artillery.com