Human wizards are few in numbers, but there's still more of them than Archmages.
There are several factors we don't know. Relatively few human wizards are Enchanters ableto make moderate complexity enchantments, but making simple enchantment may be a skill that all High Mages* learn over the centuries. There may be more human wizards than High Mages, but there could well be fewer available sufficently competent Enchanters in the College with the fewest of them than the Archmages that between them Ulthuan and Lauelorn can make available.
* Note as well that the Stone Flower doesn't require an archamage, it requires a caster capable of High Magic. All Archmages may know High magic, but there could well be quite a few elven wizards capable of very basic High Magic who aren't (yet) good enough to qualift as archmages.
It's the reverse engineered storage that currently requires archmage level skill, which seems like a different thing.
It is already very impressive to anyone who is not Ulthuan, it has far more functionality compared to the present locally sourced Bretonnian alternative of Nothing Flat (TM). We are not competing with the Golden Age since they can't make Golden Age stones. Also increasing complexity makes it more likely it will blow up with low enough rolls.
We also want to impress Ulthuan though. And does increasing complexity make it more likely to blow up?