Your correct in that my statement doesn't quite get to what I was trying to say. They didn't hate each other.....however, they both had the same chip on their shoulder and were competing against each other for who's team it was going to be.
https://thehockeywriters.com/buffalo-sabres-next-captain-eichel-or-oreilly/
Jack has always been trying to prove he was better than McDavid. Its ego. Its not a bad thing, it is a great motivator. McDavid had already been named captain, and Jack wanted to keep up. I am sure it was discussed as part of his contract negotiation.
ROR wanted out of Colorado because he wanted a bigger commitment from the team and a leadership role.
Ryan O'Reilly Finding the Home in Buffalo He Never Found in Colorado
He made it clear when he came here he was looking for a long term commitment as the leader of this team. The Sabres gave him the contractual commitment and ROR was expecting the team to be his after Gionta. The Sabres then did the same thing Colorado did and when the time came they hedged their bet and failed to commit, because they had their generational talent in Eichel who wanted the team to be his.
Jack was competing against ROR....not with him. The Sabres should have just given ROR the captaincy at the start of the 2017-2018 season and he would have killed himself trying to prove them right instead of losing his love for the game. Its not Jack's fault management let him hold them hostage, but he is not blameless.