The thing is, with Brawl+, some people grew tired of the meriad of change. However, there was simply no other way of doing things. Much of Brawl+'s progression was directly connected to what we had available to us, what had been discovered, and what was possible at the time. We were so limited, for so long. Even the line limit was a problem for a good while. Heck, we thought we were near the end of Brawl+, because of the impending line limit, and managed to squeeze in very few character changes. One, a nerf to MK's whorenado, and second, "thick skin" for Bowser. Those two changes came after a ton of time spent making the mechanic changing codes that defined Brawl+. There was also a considerable amount of time taken to convert already made codes into equiviliant ASM versions that took up less lines. This alone prolonged things. Eventually, as time progressed, and the line limit was forever removed, we saw a slew of character balances enacted. Then, after many of these changes, after so much work, PSA came out, and opened up a new world of possibilities. Many tweaks, both big and small took place in Brawl+ thanks to PSA, however, some people grew tired of the long-winded design process. Veril, now in charge of Brawl+, in attempts of stabilizing things once and for all, is no longer making many changes, if any, to the game. The people behind Brawl+ always did the best that they could with what they had at the time.
Imagine how different Brawl+'s progression would have been had there already been mechanic codes in line; if we immediately had access to no line limit, PSA, Brawlbox, etc? For one, people would not have been so quick to whine about constant changes, and demand that a release go unchanged, as the whole process would have been far more steady.
This is why P:M has so much going for it, many of the stops have already been removed. In addition, people have even less reason to complain about changing a character too much because this project has the creative authority to do that. It's a project basing itself on past knowledge, everything that went into making Brawl+ has lead to this. I mean, we aleady have many of the major mechanics out of the way for P:M, and it's only been in the works for a mere fraction of the time that Brawl+ was. Heck, Brawl+ by this time was lucky if it had hitstun, or shieldstun, or ALR, heck, many of said codes took months and months to formulate, most of which was thouht to be impossible until it was actualized.
In the end, the future of P:M is more than promising!