To be fair MTO is trying out new merge lanes on the 400 HOVs to prevent this.
And my experience with HOVs is that they do typically operate significantly faster than the regular lanes even in heavy congestion, even if it isn't at full uncongested speeds. They don't save much if any time on weekends though as the prevalence of multi-passenger vehicles is much higher then.
Generally I'm not a huge fan, an extra regular lane is cheaper and will generally produce a better operating highway. In the case of roads like the QEW through Oakville and Burlington, they could have built a 10 lane regular highway or 6+2HOV highway, and switching that road to a regular 10 lane road would have produced much better capacity. MUCH better, probably even for transit.