I agree that melding is getting excessively more expensive as stat gaps get higher and higher. I think the materia system in a poorly, lazily designed system. I don't particularly agree with the idea of perfect quality. If they introduce perfect quality then nothing will have changed: PQ will replace HQ as the new gold standard and NQ/HQ will be considered failures.
The issue with the current HQ system, that the stat gaps have made blindingly obvious, is that NQ is more or less another way of failing a synth. A synth that was filled to 98% HQ and a synth that got to 1% HQ should not have any potential to produce an identical piece. Something as simple as 100% HQ representing max stats and materia being used as a post process fix to get it to 100% in a manner akin to the Novus weapon would work. If they use the Novus template then the stat values on the materia wouldn't matter. So maybe a 1% HQ piece would need like 25 Craftsmanship materia (5 of each tier), but at 20% it needs only 20 (5x I-IV) and maybe at 80% it'd just need 5 tier Is. Once again similar to how the Novus scrolls require higher tiers the higher up the stat goes.
If they must keep the materia system in then at the very least something like this would seem more logical. Frankly, I'd rather them scrap the RNG melding system complete and just treat materia like gem socketing in any other competently designed MMO. Any piece (even token gear) can be socketed with gems. Then instead of balancing crafted gear around materia melding they can just have crafted gear with their own fixed stats that are directly comparable to token gear without requiring min/max melding to make the missing stats.
And ffs what is the point of having an ilvl if the stats on the gear is completely unrelated to the ilvl on the piece. As you pointed out some how HQ i150 White gear have essentially the same stats as NQ i170. You'd think the ilvl should change with quality and the addition of materia?