Without a switch, I dusted of the PS2 and regave them a try.
Both games are in(famous) for having a headache inducing plot. But, IMO, Xenogears handles itself much better, if we forget some cost cutting measures on Disk 2 (euphemism...). While using rather poorly mysticism and gnosticism (a tall order, considering that those esoteric theologies were almost openly made as complex as possible in a elitist perspective), the plot is extremely ambitious but make actual sense. While Xenosaga have the traits that make (IMO) FFXIII and FXV so annoying : barrage of made up terms, people droning on the abyss of nothingness and the time compression....
What I mean is that Xenogears had many flaws but an actual rock solid idea (God and Eve are both real and do exactly what they are supposed to do in our theology). Like, in fact, Evangelion. While recent games that are a bit simpler plot wise fare better, Xenosaga is almost the nadir of JRPG plots-it sounds prententious and it's barely understandable even with a Wikia and a guide.