The omega stack upgrade recipe is too expensive and mathematically makes no sense as 64x16^9 = 4.398T which is much higher than Max INT and not achievable.

A better recipe should be:
4 16x Stack Upgrades
2 8x Stack Upgrades
1 4x Stack Upgrades
1 2x Stack Upgrade
for an exact 2.147B max stack size.

BAB
A#A
CAD

(((64*16^4)*8^2)*4)*2 = 2.147B

Well, the part of this is also that you're only using 1 upgrade slot for this upgrade instead of all the slots you would have to without the upgrade and it also allows stacks larger than max of 216k in Chests / regular Barrels / Shulker boxes. So the upgrade is really powerful and I don't intend to change its recipe. Happy to discuss more on Discord if you want to, but the recipe can also be changed by modpacks so it can be made less expensive there.

I understand, I only mention it because if playing on small modpacks, without any means of increasing yield from ancient debris, the Omega Tier Stack Upgrade for the backpack requires 2,592 Ancient Debris to obtain.
That's 648 Netherite Ingots = 72 Netherite Ingot Blocks

It just seems excessive and like an impossible task to obtain such a large amount, in mostly vanilla modpacks.

Either way, I understand leaving it as-is since MOST modpacks make obtaining Ancient Debris trivial, on top of increasing scrap yield.

I'll just make a datapack recipe change then.

See in packs where this seems like an impossible task I would always find that there wouldn't be a real use for this upgrade - like in vanilla like modpack getting 216k of even just cobblestone is a huge task and that would only fill one slot of storage upgraded with 2 netherite upgrades. On the other hand as you mentioned there are other packs where netherite is way more trivial and there I almost feel like it's not expensive enough. So I like its default price.