All I can tell you is that your logic is not correct and your assumptions are also not correct
First of there is no evidence of 12 000 000 active WoW subscriptions, and if this is a correct number there are still a lot that are used by goldsellers and alike. Also subscriptions from China, where WoW is now banned are counted ... but lets say there are 12 000 000 active subscriptions and on all of them at least one level 80 character that DO try to enter raids.
Now first:
589,850 / 12,000,000 = 0.049
And this equals:
4.9% ...
Second:
According to wow progress there are currently 23 594 guilds that have killed normal beasts (actually there is one more since last time you checked
) and you say this is approximately 589 850 players. Well no. I can assure you that there are much more than 1 account per guild that has completed it. It is save to assume that approximately 35-40 accounts from EVERY guild has experienced .
Third:
There are TONS and I mean it TONS of characters that:
1. Are in a guild but only a few have completed TotC or killed a few bosses and thus the guild is not listed.
2. Are totally guildless and still have completed TotC or killed a few bosses.
They are so much that if we are talking normal beasts only - the numbers should increase 2 to 3 times.
Moreover according to wow progress 30796 guilds have killed beasts 10 men normal - this is still the current end game raid instance.
If we consider all of the above we can actually safely presume that 10% of the active wow accounts (if not more) have raided in TotC.
Finally even if 4.9% have entered TotC and killed beasts 25, this is still FIVE TIMES MORE than the percent that supposedly went in Naxxaramas 60.
And if you still think that "raiding in WoTLK has an extremely similar % of playerbase raiding as what Vanilla or TBC did", I have one thing to say:
ORLY?