The new slot system is an excellent way of slowing things down and I think it's a great move. In many previous worlds, players would have double figures of medium/large aircraft on order by now, but now things have to be budgeted much more carefully as C-checks etc come around. I can imagine many players skipping C-checks because they've splashed out on slots and suffering with hits on their CI.
Slowing growth early on has been a problem in every world and it keeps things exciting and interesting for longer.
From looking around it also seems to allows players at smaller hubs to build up their own little empire, adding routes more quickly than the those at the larger bases.