If a 350ms click delay is actually a performance bottleneck on the app you are building, it's very likely user scaling is something you want disabled anyway.
The underlying issues are that
(a) it is hard to make touchstart/touchend act the same as a native click event (touch-scroll interactions, different fat finger slippage, text selection, press duration, etc).
(b) you only want to do this for iOS and not any other browser (different browsers and OSes and pointing devices introduce a huge number of other issues: cant prevent the click on the touchend, mouse or pen support is difficult, avoiding ghost taps https://www.google.com/#q=ghost+click+tap ).
(c) you run into future compatibility problems (pen, force-clicks, other HIDs).
(Yes, there's accessibility zoom, but I didn't know about that until this thread)