As with all things in life, it requires balance, saying large maps are for these people and small maps are for these people I believe not for the best.
another way of looking at this is that small maps require more micro and therefor suite a higher skill, and larger maps require more macro wich is something most players are familiar with.
lower skilled players can manage eco and these sorts of things but do not understand how to best use those units when they have been made, for instance i often see 1k players make rocket bots but then just suicide them in with t1 ect aswell as undertsanding that flares can beat mech marines but if microed the opposite can be true this is not a low level thing.
small maps mean that the loss of every single unit counts and could mean the differance between winning or losing whereas on larger maps there is more room for error.
I believe a map size that would provide the best experiances would be 10-12km
the only differance i can see in skill required for a map would be how much water there is, having a third factor to manage ontop of air and land would increase the challange, even more so with faction diversity, low players would struggle when their opponent spams zues or aeon t1 tanks on a navy based map when they are uef or cybran.