I think we could all agree that regardless of the specific merits of Glasgow and Edinburgh as shopping destinations, Glasgow is generally more attuned to the needs of a destination for an islander visiting the mainland, not least in terms of social, health and commercial links (current and historic). But if I was going to try and persuade a tourist to fly to Islay I'd rather try and persuade them to fly from Edinburgh. (Edinburgh may also have the political links, but I can't imagine they are strong enough to generate a lot of traffic).
I'm genuinely fascinated to see how this resolves itself. If I were Loganair I'd have been too cautious to want to risk unsettling the status quo (I do think the answer will be messy and complicated). Stornoway might be big enough to support flights from both Glasgow and Edinburgh, but of course Stornoway has 4 times the number of passengers.
It is definitely wonderful news for the tourism industry, though. I hope it is marketed well!