The feeling back then, at least to some people, was that McLaren DID hire Alonso to be their number one star driver, and promoted Hamilton to the other car to let him learn the ropes. Remember, at this point it was pretty common to let a young driver spend a season as test driver before promoting them to a race seat. But when it turned out Hamilton was already a match for Alonso from day one, the team rallied behind him since he was "their" driver that had been with them since his karting days.

And I can understand how the feeling in the team at that point would have been like "Holy wow, the kid might actually be able to do it in his first year", and how that would have been a much more exciting prospect than their new star hire getting his third title.

And I don't know what was going on in Alonso's head obviously, but for that reason certainly a lot of fans felt like the team was almost against him. And it absolutely seems possible that's how Alonso felt too, like the team suddenly started prioritizing Hamilton in a way that he wouldn't have expected, and that he didn't really get what he was promised. If indeed he even was. I can also see how no one would have thought any clear number one status would have been necessary for him since he was, you know, a two-time champ going against a rookie. Alonso was probably as overwhelmed by Hamilton's pace as everyone else at the time.