Yes, Tornado can do Mach 2, but not for long, it would soon be out of fuel, it would be cruising slightly faster than Harrier (Mach 1 territory)
In terms of Libya the Harriers would have been there hours before a Tornado shows up, plus they can be based nearer the action more easily anyway, so that argument doesn't hold any water,
So what it can bomb one/two less houses on one sortie (it usually actually means they drop slightly less ordinance on the same target), but it's higher availablity counters this, you are also forgetting that the Typhoon is due the same capability as the Tornado soon and can carry more and is faster than the Tornado.
So I would have kept the unique abilities of the Harrier, it would have done fine in current situations and let Typhoon take on some strike responsibilities as it becomes available.
As it is we now have two platforms that in terms of strike, do exactly the same things - clever!