I had a convention a few months ago and had the game running on Mac and Linux without any problem so should work fine on Steam. I can't really talk mobile since i have no experience but heard there were some difficulties for some developers. However, there's the new runtime coming very soon that brings significant performance boosts as well as running in a web worker to avoid any glitches coming from the chrome browser. Check out the recent blog posts for more infos.
So Construct is a HTML5 engine with all its pro's and cons and as with any engine you have to be aware to optimize where you can. BUT of all HTML5 engines it's surely the fastest and most advanced one so give it a go and see how it works for you. Personally, i totally love it and it enabled me to make my game (in progress) and am still in awe how many things that are quite complicated i'm able to do that would've probably been impossible for me as a non-coder in that short amount of time in any other engine.
I will release my game on Steam once its finished and am pretty confident it will all work out well. I'm from the adventure game scene so i really only know games from that area but there's "The Slaughter" and "Tokyo Dark", both of which are available on Steam. I think the Slaughter has a mobile version as well.
I won't lie though i have heard some things that make me uncomfortable as well such as Streamers having trouble with nw.js showing up correctly with various video capturing software. Since my game is probably around a year off i hope that such things get gradually less. So yeah you win some you lose some but for me i think the positives outweigh the negatives, at least for this particular project. There is no perfect engine and i would evaluate them depending on each project. If you're a beginner, then i would suggest making small, gamejam style games at first anyway and for that Construct is more than perfect :)