but it is completely ignored
Just to clarify - as in it cannot transfer when slamming? Or or as in the fact that it is sealed is irrelevant and can transfer as normal?
If it’s the former, you could seal an undesirable affix to improve your odds, no? If it’s the latter, would you be able to seal a desirable affix and then play the lottery with Runes of Removal for undesirable affixes?
The legendary creation process has no knowledge of a sealed affix in any way shape or form at all. For all purposes, it is as though the sealed affix does not exist at all. It is completely ignored for all requirements and uses. You can pretend that it doesn't exist.
So, now that sealed affixes don't exist. The exalted item needs 4 affixes. If the unique item has 1LP, it has 25% chance of hitting each affix. Nothing can change that.