But to some extent those basic stats are what value is based on. Hader, and many others, can complain about arbitration trashing them because it is based on saves, but what about free agency? Saves and closers get paid. Arbitration is largely based on what similar players get in arbitration, what guys are getting in free agency, and what those guys are getting paid for.
Now...these days there is a bigger push for advanced metrics getting paid, so I do think the system is starting to get outdated a bit. Sucks for the player if the team uses them in a way that doesn't maximize their value (not using them against LHH or not getting saves), but that is what it is. If you have a problem you got to go to the team like Hader seemingly did.