I'd take a mono-culture over terrible IE (6-8) any day of the week. The problem was never a mono-culture - the problem was IE6 was closed off to non-windows OSes, and stopped progressing. If IE6 had been available as a portable open source project that could be run on linux/android/anything and had continued to include new features, we'd all still be using IE.
The problem with IE was failure to provide value, and nothing at all to do with some mythical 'mono-culture' argument. You can say that a mono-culture encourages something like IE6 - but since Webkit is open source, that can't actually happen.