How much worse is Zibai with C2 Xilonen compared to a C4 Illuga?

So i really am not too enthusiastic about building Illuga since he will probably only ever be useful to a few characters (1?), he seems so hyper niched he just doesn't seem worth the resources.

I was looking over my options and have been using Columbina, Gorou and C2 Xilonen and it has been working pretty well, Xilonen's healing doesn't work since there are 3 geo characters on the team but her C2 geo buff is nice because it's always active even if you never switch to her.

But looking at Illuga's kit it sure seems like it provides substantial (but confusing) buffs to Zibai, so just how significant are these buffs compared to Xilonen's and is he worth building without his C6?

Any Illuga and Xilonen C2 havers here that have compared the two?