So if you were facing a brown bear in the adlers at 10ft would you rather have their recommended 300 WM with Swift/Barnes or a 416 Ruger with 400 partition? It would take me about one mili second to make my choice. But I wonder what they'd choose in that moment?
To go into the alders looking for a brown bear is foolish in my opinion and If the outfitter has got you in this mess in the first place, you chose the wrong outfit. There job, first and foremost is to keep the client safe. I believe like you, a big bore is best and that there is no such thing as over kill when hunting something that would/could add you to there menu.
All of this is just conjecture and ultimately the choice of what brand, caliber and bullet weight is the shooters, and the outcome becomes his responsibility if he choses the wrong bullet, caliber or outfitter.
Outfitters are not always right and sometimes the client has to step up and say something, If that doesn't work, decline the hunt and demand you get your money back. The best chance to have a bad trip, is to go along with poor planning and bad decisions.
Just an opinion
J E CUSTOM