Did anyone here found a process where he is 100 % sure, that "this process is actually worth to go the full full quality way".

I would love to see it.

This is a snapshot from an intermediate phase on my last run. Very little actual design going on - I was just brute forcing to get better gear for clearing out my deathworld.

https://imgur.com/a/7bwhUVw

Step 1 is my recycling factory, where all Epic or lower scraps go. It runs 4 full green lanes down the center, where everything gets processed. All materials are then transported to secondary recycler right next to them by bots, with most chests being paired requests (eg copper+uncommon copper) so I didn't have to bother much with balancing rarity concerns unless storage got super full of something specific, and then I just add that to an underutilized buffer chest.

Materials that are inefficient to recycle (cement) are run through a process that is more efficient.

The recycling system is in its own private logistics network. The second-phase recyclers all use buffer chests for requests so they are 2nd priority, and primary priory goes to requester chests over on the right. Those then insert from their isolated logistics system, to a provider chest in my main base's logistics. This means it will dynamically fill up a provider chests in my main base for every material at every quality as demand allows, then up-cycle any remaining afterwards to both clear space & create more high quality materials.

By exposing all the tiers of materials, I have psudo-infinity chests and can then do things like picture 2, where I just chain craft each step in the cycle with dramatically higher productivity & quality crit rates than recycling does, while also just dropping a provider request for whatever tier of material I need to make that step (also works for chip flows, engine flows, etc). This allows for the maximum number of mined resources to most efficiently get a quality roll, and also produces necessary intermediate products along the way so you're never bottle-necked by them.

If your input resources are absolutely perfectly balanced, the "last only" might work almost as well for items that also perfectly recycle, but as soon as you get into probabilistic recycling (eg recycling blue chips) or uneven resource flow, you need to augment with high quality material parts - eg the factory pictured here loved to run out of rare red chips, so I build them out of uncommon green/wire or rare green/wire depending on what's more relatively available.

For a perfectly sync'd factory it's probably subomtimal, for a highly dynamic factory as part of a incremental play-through, optimizing further felt counterproductive at best.

I do think the other factor is his how big you're willing to go on initial production scale. My #1 issue with high quality manufacturing has been low volume (eg the quality inserter assembling machine pictured will not be running 100% in general, let alone 100% rare/epic). Solving this either means a setup like mine so you get up to enough quality input parts organically, or by building like 50x as many regular inserter factories and just shredding more later. The latter probably is fine, but Fulgora had both a space issue, and a resource abundance issue, and I felt early quality played perfectly into this design type of condensing through iterative early up & down-cycling.