De Jong was just an example. He, like Mount, appeared to be our primary target, or at least the first player we were publicly in for. Replace him with Fabregas, Vidal, Sancho, Kane, Onana, Kim Min-Jae. The point I'm making is, if we were 5% away from one of our priority targets, the responses wouldn't be "walk away". With Mount there appears to be something the fans are put off by. The contract situation, which is the only reason this deal is even possible, appears to be hurting the fans reception of the transfer.
The negotiations haven't been perfect. I don't really agree that us paying an extra £5m for Mount will significantly drive up the prices of all future transfers. I think we are already paying a hefty premium on most transfers anyway. But by making the "take it or leave it" offer, we've created a situation where if we pay £50m + £6m then we've "lost" the transfer. We're signing one of Chelsea's prized possessions and have somehow turned that into a negative. If they'd came in and signed Rashford, I don't think our fans would be counting that as a win under any circumstances.