Servo Wave is a Shimano trademark about how they have arranged the leverage on their brake levers. It goes back to the 90's long before hydraulic brakes. They didn't say it much in the 2000's but brought it back in the mid-2010's. They don't do a great job explaining it. It doesn't have anything in particular to do with the 4 piston calipers.
I think your goal for this bike should be to get it running well so you can go ride, not get hung up on how premium the parts are. Your supposedly clapped out brakes, is there anything wrong with them that a bleed and new pads and a cleaning wouldn't fix? Do they even need new pads, for that matter? It takes several sets of pads to wear out a rotor. Unless there's exacerbating stuff like downhill use or mud, pads can last thousands of miles. If the brakes are actually leaking it's a different story. You can't always get maintenance parts for cheaper components because they are just so cheap to just swap out.
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Genesis 49:16-17