Many times Star Trek has taken us to the future only to reset the status quo at the end of the story arc. Tapestry (but in reverse?), that time Voyager crashed in the ice, and all that.
How likely is it that Discovery went to a mutable future, just one of many, especially with the Temporal Cold War, Carl, Q, Trelane, Janeway, the HMS Bounty, and any number of other temporally active agents out there in time? How locked in is the 32nd Century?
But removing Discovery from the timeline seems to be consistent with the prime timeline post-Discovery season 2 (in TOS etc) - e.g. Spock not talking about his human adopted sister, no further use of spore drives, and so on. It’s certainly explicitly the timeline of SNW (which makes multiple references to the events of Discovery s2) and therefore the timeline of Lower Decks.
That suggests the prime timeline as we know it is an altered timeline caused by Discovery’s jump to the future.