A potential solution to item level syncing & power creep:

[Jeeqbit]

If you currently synced the iLvl 495 Chest to iLvl345: Vit +113, Mind +124, Crit +123, Determination +123 (You are getting extra substat points here for the second substat!)

In exchange for not having materia.

There are many factors that affect this and I will try to list as many as I can for you.

1. Potency adjustments.
2. Accuracy being replaced with Direct Hit.
3. Parry being replaced with Tenacity.
4. Determination's effect being increased.
5. Strength being added to tank accessories.
6. Stat allocation being removed (you had some stats to assign as you level).
7. Tank damage reduction becoming a trait so you can't turn it off.
8. Vitality being on all accessories, in exchange for it being worth less and a trait increasing it for tanks.
9. Higher level food being more powerful than it was at the time (but I think the stat squish rebalanced this).
10. We currently gain 5% DPS for having 1 tank, 1 healer, 1 magic DPS, 1 ranged physical DPS and 1 melee DPS. I don't remember if it used to be as good. I remember it affecting stats useless to most of the party like VIT and DEX.
11. Dungeon boss health was nerfed at one point (and I don't know why because they died too quickly already).
12. Stat squish.
13. New jobs with higher potencies.

I don't think that there is one way to make it how it was. But you can try by intentionally reducing your item level until it feels right.