The more the merrier
The argument that Microsoft could make a browser totally from scratch faster than just basing one on WebKit? I think this is probably nonsense. HOWEVER:
"Moreover, he said, Redmond is concerned that other browser makers' reliance on WebKit is creating a "monoculture on the web" – something that today's Microsoft is apparently against."
This is 100% true; with Chrome and Opera using Blink (WebKit-derived) and Apple & KDE using WebKit, you're down to like WebKit, Blink and Firefox engines dominating the browser market share. It is "healthier" and overall better to have more independent HTML implementations than fewer.