I suppose my biggest fears of quantifying mana is ensuring relevance and fairness. That is to say that mana quantities should be not so low that it cripples mages, but not so large it is completely irrelevant. There are many ways I've seen people try to suggest we do this over the last decade, from numeric mana (as suggested here) and spell slots (full DnD). Someone earlier mentioned the TTRPGification of LotC: seen in less freeform magic, the numeric values given to many abilities (mana equivalents and such) amongst other things such finer rules on armour, weapons, speed and so forth.
There is definitely a balance needed, something that no doubt will be created through the great amendment war ongoing. I had liked Primnya's but on thinking about it more I feel it still doesn't hit that perfect note. Perhaps we're thinking about the numbers all wrong or something.