Do you have a link? I am not aware of many 3-XML 26650 lights.
this one should probably be avoided, unless you aren't expecting full brightness from each XML.
https://budgetlightforum.com/t/-/2821#comment-112576
I have my eyes on the skyray 856, but I'm not in any hurry. I would still expect each XML to only be moderately driven in a light this small.
https://budgetlightforum.com/t/-/7758
A single XML driven to its full potential in lights this small will need ~9 Watts (3A @ 3.2V). Three bumps that to ~27W. A single 26650 can't hang with that kind of demand, and even with two in series it's pushing things.... IMHO. So, I would expect 3-XML 26650 to be somewhat under driven, although it should still have more/greater potential than the same number of 18650 cells.