V8 is ACTUALLY fast and has been for years. I don't know how that could even be contested. Mozilla internally knows that v8 was/is fast and has been trying to beat them.
Chrome does use more memory if you have a ton of tabs open, but it also is still fast. I haven't noticed a substantial amount of memory leakage, but I guess that depends. Regardless, the memory leakage can be subdued by reopening a tab rather than reopening the app.
The marketing that Mozilla puts out is the problem, not Google's marketing.