"but if so then why were the original terms shit (or for a nicer...

"but if so then why were the original terms shit (or for a nicer word, "not good enough") when the project has always seen upward revisions to the DFS since it was released? "

I think the answers to that are multiple and easy to guess.
The main cornerstone investor has an interest in our phosphate. There is nothing wrong with that but they might have wanted a bit too much say in how much we sell to them and at what price. Perhaps the company sees better value in exporting as a fertiliser or wants to keep that option open. Or it might give the company better negotiating power to be involved in P4 production rather than just supply the phosphate for P4 without exposure to the value add.
Also as any investor would often do, the cornerstone investors might have wanted attaching options or shares as part of the terms which increases their investment but dilutes other shareholders. I don't believe Export credit agencies ask for shares or options when offering loans. Loans are on reasonable terms because they are government agencies without a greedy self interest.
Loans from any bank are always going to have much better terms than a loan from investors that will probably want to maximize their return beyond just interest payments.
If we had no better choice, the loan from the cornerstone would have still worked and got is into production but the export credit agency loan is likely to be much better for us.