I can grok 1. It's just that in Star Trek, this never affects anything, and never amounts to 2. If the world suddenly looks like TNG, TOS still happened exactly like it did. If it looks like Kelvinverse, TNG and the TOS movies still happened exactly like they did. This is made explicit in the respective spinoffs.
Now, this thread is not about that phenomenon. It's about a different premise, as you make clear. It's just that the premise is somewhat alien to Trek, which might confuse the audiences.
Ookay... So, what would be different from TOS ten years down the line when DSC spilled over to the 2260s? That is, being dictated as being different by DSC? Not the uniforms - they tend to change overnight anyway. Not the sidearms - same deal. The more permanent fixtures such as ships, perhaps - although the "more varied designs" argument already covers that, since TOS didn't show us anything and thus didn't dictate or contradict anything. The hero ship could be the same, that is, become the same. The holotech? If anything, it's more advanced in TAS than in DSC. The forcefields? Same deal, they become invisible by TOS.
So basically I'm having to state here that a lot would be different, that is, different from DSC and thus perhaps similar to TOS, because that's how Trek usually works in the timescale of decades. Which is disappointing for the thread, alas.
But if nothing was different from DSC, then the thread becomes duller still: TOS is just DSC, in a differently shaped ship but otherwise with the DSC props and aesthetics. I can't see the plots affected much either way.
Timo Saloniemi