I understand that part and it makes sense. The only thing that stands out is the amount of power we are talking about. I mean, the description of the amount of source drawn by Kal seems to indicate a lot more than anyone at any point even dreamed of. Seems to me that LTT would not be able to draw that much power, even in the "raw" form, without any aid.

I don't think LTT drew near as much power, even when he overloaded, as the CK would allow. Its been stated several times that the CK could crack the world in half... and while I don't think that's meant literally, I do think it implies that it could a lot more damage than forming the Dragonmount.  The times we see CK destroy land, that's merely a side-effect of doing some other thing.  If Rand had realy turned the full force of the CK to destroying the Dragonmount, I think we'd see a lot more than the top of the mountain destroyed....  I suspect the destruction would wipe out Tar Valon, parts of Andor, etc.