Yes Mahoney went there when no-one else wanted to go there, he also accepted what no-one else was offering to do so. Dogs owe him nothing in my opinion, even if I agree he was pushed out. Fairly? Maybe, maybe not. But that is the game nowadays. Now, yes, he was seen as a core member of the side given he was a co-captain prior to Crichton's arrival. I've only ever heard how it was Crichton who changed the culture. I don't think I've ever really heard anything positive about Mahoney.
The others however:
Sexton was given his contract and it seemed to be clear from day one he was only ever seen as a temporary solution to them.
Xerri I don't believe has ever been told or perceived as being core in any way. They got him on the cheap due to his time out of the game. The arguments rightly or wrongly about our players being moved on could be applied to him.
Burton is still there. Is currently still key to their success and whilst long term looks to possibly end up being the odd man out I don't see him getting pushed aside prior to his contract expiring.
The only difference I see is our results were terrible so it's deemed fine to push them out. Dogs were having some success so despite their management believing they are upgrading the team it's suddenly not ok.
As for someone seen as, or communicated to as, being core. I'll raise you JOffa. Went from Player of the Year and upgraded and extended one year to pushed out 2 months into the next season. Again cap management perspective potentially understandable but as ruthless against a player as anything that's happening at any other club.
So again I see Dogs as no different to anyone else in how they treat players.