The final tier requires absolutely ABSURD quantities of science packs. Why in the world?!? No structure in the game needs more than a few thousand packs just to research how to make them. Even the Space Age tier 4 belts only need 500 Metallurgic packs.

It's bad enough that you need to go all the way to Promethium and gather up science packs from every planet in the game in addition to that. But one hundred thousand of each one of those?!? You gotta be out of your mind! xD Usually the roadblock is actually getting to the point where you can DO the science, not spending an eternity farming them before you can even know how to make the belts.

A more vanilla-friendly tech progression might be:
tier 1: 20 packs
tier 2: 200 packs
tier 3: 300 packs
tier 4: 500 packs
tier 5: 1000 packs (not 4000)
tier 6: 2000 packs (not 10,000 D:)
tier 7: 4000 packs (not 100,000 o_O)

As one other note, I noticed that your tier 5 belts don't actually require the tier 4 research to be completed. So you could technically research the tier 5 without even researching the tier 4 at all, which feels a bit awkward. The internal name of this technology is "turbo-transport-belt" for your prerequisites section.

It's an end-game goal. The vanilla experience only has a single promethium research.

Yes, it's expensive, but what else are you going to spend the science on?

I know someone who plays at 300x research costs, 100k science is nothing. :D

As one other note, I noticed that your tier 5 belts don't actually require the tier 4 research to be completed.

Fixed in 2.3.0

as a fellow vanilla++ modder, i say the 100k cost is fine

I have a custom version of the Mythic Quality mod and made the cost of that 1million of all science packs.

The key is scale @TimmetryPM, the factory must grow. :)

just take a look at stuff like https://mods.factorio.com/mod/UltimateBeltsSpaceAge?from=search, if you can add more contents to your belts. I love super fast belt mods lmao ty

I made this mod because I didn't really like that one. Plus there is an upper limit on belt speed, over which you'd risk voiding the items on the belt as from one rendered frame to the next they would just vanish. So 5 new levels? Naw, 3 is enough, trust me, use the config setting, set the top tier to the fastest option and be happy you have the fastest base in the 'verse.

Combine this mod, with my other mod
https://mods.factorio.com/mod/infinite-belt-stacking-fg

And rejoice that you can move more material faster than a star trek teleporter

will take a look, many thanks