It is literally not a high number, but to be generous, let's say there's 800 accounts right now with the Dreadnought mount, let's be generous and say none of those people win-traded or benefitted from anything 'unfun' to get their mount and every single one is an individual account with no duplicate entries or spots. Now to be unfair let's compare that to purely live active accounts (as of 4 months from what I can tell) and the total amount of all accounts registered (including unsubbed, bots, alts, whatever else) for a full picture as Dreadnought was in Feast 20 and near as I can tell that was the last Feast and thus the one with the most winners possible.
First up, that's 0.004% of 17,356,853 total active accounts (public) and would only get smaller and smaller if you were somehow to track non-public active accounts as well.
Next that's 0.002%, so of 30,000,000 accounts (as listed in the 'last 10 years' statistics released) only that miniscule fraction could even feasibly have a Dreadnought.
According to those same statistics the majority of players started during Shadowbringers which means a majority of players in the game never even had a chance to compete for the Hellhound set let alone any of the other earlier Feast seasons, that's pretty bull if you ask me. Now to throw more numbers I've seen multiple websites claim that there's about 51.1 million total accounts which would drop the total playerbase percentage at 0.001%, talk about a big OOF right there, now looking at Feast rewards multiple seasons had armors and many more had mounts, each one is theoretically locked to only 0.002% of players. Further let's look at monetary support as a fun little side thing, let's say maybe half of the total accounts are subscribed, in a single month half the total accounts (15,000,000 players) bring in 224,850,000.00$ USD (assuming a standard subscription fee for a single month), of that a meager 11,992.00$ USD comes from all 800 Feast players. Legacy account numbers aren't really available so I'll just use the Legacy Chocobo numbers from active accounts, so that's 3,305 right now (from public accounts or whatever FFXIV Collect tracks), those players paying a Legacy subscription fee of 9.99$ USD bring in 33,016.95$ USD per month... so not only are Feast rewards undeservedly limited but they're entirely trophies for a fraction of the possible monetary support they generate, does that make sense?
Feast top 100 players make up less than a fraction of the total playerbase, generate less than a fraction of the total revenue, and get MORE special rewards than actual Legacy players from 1.0 got.
Again, does that make ANY sense to you?