maybe the term itself (seeding) isn't the one used by programmers. Maybe I should have called them "pools" or something like that, but it would be 2 different types of pools in my explanation.
before going into semantics, I am not a programmer. The explanations I try to give are from a lot of discussions about RNG in F2P games I played, and should work for many other game relying on RNG
First, many games do not really rely on RNG but pseudo-RNG (PRNG) for a good majority of them. Nearly the same results, but not the same way of working.
They create a huge pool of numbers, and then take a sample of these in order to create the loot pool. That loot pool may be reset under some circumstances (here starting a new fight maybe ?).
Though, the loot pools do not take evenly values for every prize. Even if a sword has 10% of the values, the loot pool may only take 5% of "sword values", while taking 3% of "mount value" while said mount only has 1% of the initial values.
What I called "seed" is the pool of numbers taken from the initial pool
(after further searches, it's not what a seed is in programming. Well, ignore the word.).
Also, the numbers are totally made on the spot. A 1% item can't get a 20% drop chance in the loot pool. Even with PRNG it would be the once in a century occasion.
on an other hand, instead of blatantly saying "you're wrong", maybe next time you could develop ?
Oh and btw, it's not totally accurate, but here are the numbers about how many mounts there are in game :
http://xivsoul.com/
you can see that the numbers aren't accurate with the "0 players" in the 3 last created servers (Jenova, Zodiark and Shinryu). (Also, it can't see mounts if the lodestone profile is locked)
also, you shouldn't overestimate the number of people who farmed the tank mounts... It's plainly stupid to farm for something like that >_> you'll get it over time
Still, it gives an idea