Is it backed up by the CAA stats?
It was discussed in the Southampton thread. It's hard to extrapolate the Glasgow stats as to who is winning that battle. A modest increase in pax numbers considering the additional capacity and only anecdotal evidence otherwise with people saying easyJet's look full when boarding and others saying easyJet are averaging about 100 pax.
Similar with Edinburgh - Southampton. November's figures were 15% down year on year but for most of the year the differences are marginal when compared year on year, with the summer months actually being higher. Ryanair's Edinburgh- Bournemouth started in April, didn't it?
So I would say, at the moment there isn't much evidence to prove either way on Glasgow, but Edinburgh seems to be holding up pretty well.