XI's mythics aren't really "work", they're just a slog.
Semantics. The most common reason I've read of someone not wanting to do a mythic or another is "too much work". A guy in my LS who has several current expansion "relics" in FFXIV who doesn't want to make a mythic in FFXI because of how much effort it entails. I can confirm the difference. People in WoW used to brag about completing certain legendary weapons. I completed 2 relevant ones and they were a cake walk in comparison.
Sorry to barge in but which WoW "legendaries" did you complete?
There's a lot of very different ones in WoW and the amount of work from one to another is HUGE, so the fact you managed to get two (grats, btw!) doesn't really tell us a lot.
In general WoW's legendaries, especially the old ones, took a lot of work but it was a different type of work. Closest thing I can think of in FFXI is old relics during the early 75 era.
It took someone to lead a group of people, to schedule weekly, succesful runs, to manage the drama, and to decide who gets the coins for their own upgrade.
It's not the same but... it's the closest thing I can think of in FFXI to compare to those old WoW legendaries.
If you ask me it's hard to say which one takes more effort.
And comparing it to a mythic... I mean a mythic nowadays is mostly solo work. A lot of work, sure, but despite of the new more lax time gatings, it's still something you can do on your own at your own pace.
Can't say the same for some weapons like Aeonics. You either have a group (and then it's super easy) or you pay money to mercs, or you simply will never get an Aeonic.
So if you see things from this point of view the effort/difficulty is relative and subjective.
Relics in FFXIV are sorta in the same boat. The latest versions of the ARR ones and the early HW ones were all within reach and didn't exactly require you to farm who knows what super difficult raid or content.
But it required you to grind hours and hours and hours and hours and hours of FATEs and Dungeons and blah blah, so many different contents with daily/weekly caps.
It was... compareable to FFXI mythics maybe.
FFXIV relics over the last few expansions have been different. Bound to a new type of content/story, it still requires a lot of work but it feels more... fluid, more seamless, more rewarding and less frustrating.
If someone who completed FFXIV relic feels a FFXI mythic is "too much work" imho it's because he simply isn't "attuned" with the different, anachronistic, pace and style of FFXI, or because he doesn't have enough jobs developed to a certain level to allow them to solo everything at their own leisure.
Just my two cents of course.