[quote]The forerunners moved the ark through these portals. [/quote] Which would have been made to move an object that size unlike the one on Earth which isn't made to move objects the size of HC. If it was than the portal would have been larger than HC so it can go through it without problems.

But they clearly would have adjusted the size of the portal and the strain would have been felt. Nobody could have done that for High Charity. Not to mention, if it went to Earth somebody would have saw it.