We have a mix of kits and free builds, and DS5 loves both. Some of the kits are fantastic for play, so it's a shame to me to reduce them to just bricks! But we have a lot of generic lego that gets made into lots of different things.
If you want to encourage creative building, join in. Make some extra buildings or new cars or whatever. Get different building materials (Kapla is a major hit with DS5).
FWIW, my DS is a more creative builder than I was in part because his school has free build lego in the classrooms starting for the 3 year olds. Every class, a giant pile of lego. It's brilliant for the kids.
