Is easy to underestimate how difficult it is to take people away from a market leader. A good example of this is YouTube Gaming which tried to do exactly what you described with Twitch. YT Gaming just hasn't pulled the numbers from twitch, even though the infrastructure and existing YT user base is already there.
that isn't really the main point I'm making, my point is that amazon likely has a bigger advantage/chance to do it than most other contenders... whether it is still unlikely or not isn't the point, it could be even less likely for a company without all the advantages amazon has - if there are contenders here then amazon is likely a serious one
if it is as difficult as you suggest then fair enough perhaps I'm overestimating and there are only slim chances... but those slim chances are probably better than the even slimmer chances of the rest of the potential competitors
Related to that often pulling the big names and offering them a lot of money to come over doesn't work that great either - often the audience doesn't come with them and instead they risk fading into relative obscurity.
they got some decent stuff on their prime TV service buy splashing the cash about... maybe they overpaid for the grand tour a bit but some of their other content is decent
I do wonder what would happen if they bunged say pewdiepie a few million to come over to them... I mean he's had his own beef with youtube anyway