I suggest there be an exclusion added to Worst In Bag to not count legendary items ilvl.
They are likely to be much higher level than other items and throw the system off. Consider that you may wear a legendary in your legs slot; the system would encourage you to consider other options in that slot to be low level and be sold. Then one day you change legendary items to a different slot, you now have no options for legs to replace the previous legendary item. By excluding orange items from the system you would always have a high level option to use in this case.
I’ll see if I can get you one when I get home. But your question makes me wonder, is this not the expected behavior? If I have 262 legs (legendary) equipped and 226 legs in the bank; would not the system identify the 262 legs and my BiS for that slow and thus the 226 legs being greater than 30 ilvl below them, destroyable? It could be that once again the robot is smarter than I give it credit for.
Worst in Bags should already ignore current-expansion legendaries as a reason to exclude another item (either based on item level or the “very likely” option). If you have a case where it isn’t working as intended, make a snapshot and we’ll test it out, instructions on how to do that here: