What a load of rubbish. Dermot is an experienced broadcaster, not just a "primetime presenter" and has been hosting 2-3 hour radio shows weekly since 2004. This Morning didn't just pick a couple of people from last years Love Island to host the show, they picked one of the best live broadcasters in the country with nearly 25 years experience and someone who has had a successful role on the show for almost 20 years.
And nobody starts in a role fully experienced in that role. Phil has nearly 20 years under his belt at This Morning now - but didn't in 2002. However had he been dismissed then as just an ex-Saturday morning presenter he'd never had got the chance to get all that experience.
If you asked members of the public for the programme they most associated with Dermot, it would be X-Factor. Plain and simple. Absolutely, he is an experienced broadcaster, but that doesn't mean he suits all formats. Vanessa Feltz is also an experienced broadcaster, but when she guest-hosted TM a few years ago, it just didn't work.
And, yes, Alison has had plenty of experience on the show, but holding it for 2.5hours is something else altogether.
That is not to say they are incapable of hosting the show - Dermot was good when he hosted with Holly a few times, Alison was good when she hosted with Ruth once, and Rylan and Alison was also a good pairing.
Fern had already established her place on the programme by the time Phillip joined. She is also of a journalistic background, so likely led on the hard news items (initially, at least). No doubt, Phil learnt a lot from Fern over their tenure in dealing with such topics, and this is has probably repeated itself with Holly.