The first answer anyone will give for this question is: "It depends on your design"
This is because it does. What do you hope to accomplish with Construct 2? Meaning what do you plan to build with this tool based on what you've read.
Now that that's done.
The main thing with HTML5 and Construct 2 is that performance of games will get better the more time goes on, since phones will become much stronger and the limits will be less prevalent. With my experience, mobile performance with Construct 2 has been good. I'm currently developing a twin stick shooter and there's quite a lot of enemies on screen and I've tested the game on about 20 devices so far. All of them were in the range of 50-60. Except my Galaxy Tablet (THIS THING SUCKS). I'm not supporting Construct 2 though, you NEED to be smart, clever, and skilled in order to have a good experience with mobile.
If you want to get an idea on how the performance is, you can send me a CAPX file of what you'd like to test and I can send you a ZIP Folder by exporting through CocoonJS. With the ZIP Folder, you can launch the game via the CocoonJS App Launcher.