But here's how those examples are different:
Black Widow takes place before she dies, so it doesn't take away from her death. If anything, it gives further insight to her character and adds meaning to it.
Vision isn't real, he's a recreation from Wanda's mind (as far as I can tell) created as a result of a complete emotional shutdown on Wanda's part because of losing Vision. She went from Vision's death to killing Thanos to Tony's death without properly processing any of it, and this is the result, so Vision is never really there.
Loki is problematic for the same reason as Gamora. If he ends up in the main universe (which him tying into Multiverse of Madness suggests), then it takes away from his death, especially if he's in Love and Thunder. Just like how there are very few ways that having Gamora in Guardians 3 would still honor her death in Infinity War.