>>> (Both SipML and JSSIP have more frequent packet drops on the same systems than xlite)

What kind of packet drops are you talking about? if this is about media/audio that's entirely on the webrtc browser engine which is C++. SIP signaling on the browser goes over websockets (https://tools.ietf.org/html/rfc7118), so I'd not expect any kind of 'packet drops' on signaling either.

In short, I doubt your problems were due to the SIP stack in JS.