I don't think the bolded and not wanting Carbery add up, especially considering you also cite international aspirations as a positive trait for a player and if Carbery chooses to go there its for his own international aspirations - Questioning the professionalism of a 22 year old, 10 cap international is bizarre also - and the reason he is third choice 10 at Leinster is because he's second choice 15 behind a player on a central contract, when Kearney is available Carbery is second choice to Sexton, there is literally nothing more to it than that no matter what people suggest, he is and always will be a better 10 than Ross Byrne who has much more restrictive limitations to his game than Carbery.
The one genuine, and not fabricated or misguided, worry in this post is his ability to manage a game as a starter, he failed to do it against Treviso, struggled against Fiji and has had no other 10 starts since 2016. The good news is that, back when Isa was still being used at 15 and JC was solely used at 10 he did control games well, and he did it up to European level where he started in a drubbing of Castres, the following week he replaced an injured Johnny Sexton and helped salvage a BP away to Montpellier. He hasn't lost this ability, and he's developed his skills since then, give him time and he's a far better option than McPhillips who is rumoured to be on his way out regardless. Ulster are also lacking in quantity of 10's as well as quality so I really can't fathom not wanting Ireland's second choice 10.
There's so much worry about Leinster's two tens when they're both far more experienced than Sexton at the same age who couldn't get a game ahead of Felipe Contempomi and Isa Nacewa, no flyhalves have the ability to control a game consistently at 22, its the most difficult and valued backs role for a reason.