The 60 extra substats you get from pentamelded materia on Rinscita gear is roughly equivalent to 9 Strength. So for chest and leg gear, the 620 Lunar gear is usually better.

For head, hands, and feet gear, it's a close trade-off, and you have to look at the specific substats you're getting. The priority for substats on WAR is Crit>>>DH(melds)>DET>SkS>>TNC.

That's a bit of a simplification, and you'd have to look into stat tiers and GCD alignment to know exactly how much SkS to aim for. I wouldn't worry about that though, unless you're doing Savage/Ultimate raids. If/when you get to that point, you can look up the optimal builds in The Balance discord server.

If you wanna know how all this is figured out, you can look up Allagan Studies.

TL;DR: Item level is more valuable than materia most of the time. But optimizing around substats can get you 0.5% more damage if you know what you're doing. It's not worth the time for most people though.