I get the argument that if you're Mount and you've come through the system with James and both "made it", both been good performers for Chelsea then it would be a little surprising to be getting substantially less. From a players and agents point of view that would always be a point of contention. That's how these things tend to work. You can guarantee agents are across all the detail kicking up a fuss when anything is not quite in line.
If the figures are true, it sounds to me a bit like James is getting a wee bit too much for a right back that does pick up injuries and Mount is probably underpaid based on his performance a couple of seasons ago.
I rather hope we don't want to give him 250k if we get him. There's probably some kind of medium between the two figures that would make a bit more sense for Mount's standing in the game. He's a good player but not exactly a proven winner, a hugely established international player that's done well at that level, or one of the PL's top performers over a period which to me are the kind of benchmarks where I want to be paying 250k plus. I think I'd want to give him a deal that provides incentive for him becoming those things.