I was asked for my opinion on this ATB hand. I offered my opinion but didn't manage to convince the person asking, so I said I'd solicit more views.
2C is't GF, but promises a rebid and shows about 10+. The partnership doesn't play kickback/minorwood etc. RKCB responses would be 1430. Over 4S, 4NT would be to play, but 5C isn't forward going per se.
You may not consider the methods optimal, but it's a judgment question within that context.
edit: basic system is strong NT, 5542 openings, inverted raises over 1D. 2C only guarantees 4, but with most hands with only 4 you would find something else to bid, e.g. raising diamonds, bidding a major, bidding no-trumps at the 1/2/3 level naturally, so it's usually 5+. the only time you would have 4 is for a 3334 shape with too many points for 1NT and weak major holdings.
My view was that it was entirely on south. North's bidding pretty much demands slam unless south's 2/1 was based on values in hearts. To people who suggest 4S denies a diamond control, I think you're taking this up the line cuebidding a little too literally: sometimes you have to make the cue partner most needs to hear to avoid endplaying him. If we were most interested in hearing about diamonds we could bid 4C.
The south player, who asked me, thought he couldn't do more as he had a working 7 count for his 2 level response, whereas I said he has 2 keycards, extra club length, only 3 points wasted in hearts where he could easily have more after his 3NT call, and the potential to ruff out partner's diamonds. With 6 club tricks and 2 known heart ruffs in dummy, he doesn't need much in the way of high cards to make slam, yet his partner's bidding like a train.