Quite simple really, the giants would think nothing of splashing out £50M - £100M on a player and we cant so they can afford to look at a different calibre of player than us.
If Lukaku was the finished article we wouldn't have a cats chance in hell of getting him. We have to gamble on his potential and I think he is worth the gamble
The crux of the matter is whether or not you believe he can develop, some do Haf doesn't, I am in the camp that doesn't believe he is anywhere near as poor as Haf makes out but neither is he the finished article
As for your second point I think there are plenty of teams who would like to sign him