No Time To Die should've been the final battle between Bond and Blofeld, and Safin should've been a red herring
Safin's goal is to get revenge on Spectre, but halfway through the movie he does that and he doesn't have anymore motivation after that other than being vaguely obsessed with Lea Seydoux (understandable, but still). Wouldn't it be better if it turned out that somehow Blofeld had been manipulating him, that Safin's attempted revenge backfires and he ends up freeing Blofeld? Blofeld kills him, takes over his little nanovirus scheme, and plots to sell it to the highest bidder just to fill up his coffers again. Blofeld kidnaps Madelaine just to screw with Bond, Bond goes after him, you get your classic hero-villain showdown without all this weird patter of Safin saying he's Bond's dark reflection or whatever.
I think it would make a lot more sense and fit Bond better to go down in one last epic battle with his arch-nemesis instead of some guy who just showed up and you don't even know what he's trying to do. Because once you've gone and made Bond's arch-nemesis also his foster brother, you might as well go all the way and let him be the final boss.