Are you sure?

If that were true, then Rarity 8 would, on average, be better than Rarity 7, but that doesn't seem to be the case at all from hundreds of talismans I've made of each. Out of all of those talismans, Rarity 7 was almost always better than Rarity 8.

What seems to have happened is that they basically reset the curve at Rarity 8. It used to be that skills+slots-to-Rarity was basically linear for 1-7, and it's still basically linear from 8-10 now, but there's this huge dip from 7 to 8.

Which would make sense from a game design perspective. Rarity 7 was already great. They don't want the new melding tiers to give you nothing but great-or-better talismans or the lottery/chase aspect would fall apart. They still want to give you mediocre talismans to bulk out the rewards. So they just say "8 is new mediocre, 10 is the new great".