There will be players at championship clubs that are underachieving or under-utilised for one reason or another aswell as league 2 players that are capable of stepping up to league 1, it’s down to the manager to decide if he can get the quality needed out of a player regardless of what they has previously achieved or not achieved.
As with anything a mix of approaches is possibly the best way, for instance ME once spent a fair bit during a transfer window which didn’t work so it appeared he was reluctant to spend any significant amount again thus initiating the slow decline of quality to the state we were in last season. Sensible investment at this level can see decent profits for a club IMO, I believe under ME the Harper deal if completed would have been a loan.