I see where this suggestion is getting at. It's quite nice to have some game modes that players can visit to take a break from the more competitive game modes such as Factions and KitPvP.
I can't really comment on Skygrid because I've never played it, but creative is an amazing part of Skycade - some real talent does come out of it, especially with the monthly building competition that
@nocookies4me hosts. Skycade Creative is actually now one of the better creative servers that I've seen - features such as the holograms, particles, and armour stands are brilliant and enable players to produce some fantastic builds.
Lag isn't always down to having 'redundant' game modes on the network - it's to do with plugin performance and the demand on the servers. Now yes, if 'redundant' game modes were removed, more space would be able to be allocated to the more popular game modes, but from my experience, there isn't currently a major lag issue(?) and there if this was a main solution to lag, I'm sure they'd have already done it by now.