Apologies for the confusion, what I meant is that upgrading from Legacy P2PKH would yield such a fee reduction, thus exchanges and other users would be highly incentivized to finally upgrade to both Segwit and Taproot.
It seems I also overestimated the upper bound of reductions. Going from P2PKH->Taproot + CISA would yield a 72% reduction in fees
Ah, I see what you mean.
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