I think there's hard feelings from KB about the fact that this door was left cracked by MLB. Cubs are far from the only team to do this....though I agree with every word of your last sentence.
I think it's a horrible framework. Braves did it to Acuna, Astros did it to Springer, Nats did it to Harper, Rays did it to Longoria and I'm pretty sure the White Sox did it to Jimenez this year. It was going to happen to Vlad Jr, until he got hurt and the situation became moot. All that said, I think that's exactly why Bryant should lose the grievance. This should be handled by MLB across the board and likely resolved through the CBA. The Cubs broke no rules, as shady as it was. If KB wins, suddenly many teams' long-term plans will be thrown a curve, as I assume many players would follow to hit FA earlier.