I wonder who are those "profesionnal" that say this, performances are an issue only on mobile, and even then, it is mostly with old devices (people are targetting those because they are still in use, or because publishers wants them), at the end it is.
the other issue is the wrappers, but with crosswalks getting better and better, and Ejecta starting, this issue will be took down in the long term (again, not talking of old devices).
With careful design, I didn't had performances issues, mostly audio issue on phones and tablet, but apart from that, not that much issues.
Performance wise, it is the best HTML5 engine I've seen, some says HTML5 is an issue, but why did they bought it in the first place then, is beyond me anyway, and sometimes updates improves performances, the hard part is not breaking anything by doing that.
As for the features, people are asking for them, some says "it should improve performance instead of pleasing everyone!", but performances are fine, and by implementing those features prevents people doing it wrong by themselves and complaining about performances after that anyway.
Just try it, and see if it works for you.