2. TOS Tholians open the doorway to Enterprise
The Tholians' crystal webbing, which used to be just an alien threat, is now a symbol of Mirror militarism. Its geometric accuracy is used to trap prizes like the Enterprise's future sibling. This makes Spock's story better: in the main universe, he learns to use logic against madness; in the Mirror context, his 2268 ordeal foreshadows Archer's 2155 coup, when Defiant blueprints change the balance of power in the galaxy.
There are a lot of visual references, like how the shimmering haze of the TOS rift matches the portal effects of the Enterprise. The angular threat of the Tholian ships also comes back, which helps keep things consistent.
The weaving, which transforms a mid-tier season 3 episode into important lore that links Enterprise's serialized ambition with TOS's isolation, is the best example of Trek revisionism. Watching it again gives you "aha" moments like Kirk's last agonizing transmission echoing across timelines.