@Kyno
For an alternate perspective, I've only been playing about a year. 17 relic characters (only 2 R7). I've been saving relic materials for the JKL/GML reqs that will be months in the future. Carbonite CB's are my biggest gap right now. Bronzium Wiring is next, but that's more easily farmed with better conversion rates. And my carbonite gear reserves available for conversion is low.
Now, being a comparatively newer player, I've probably had to spend proportionally more of that lower gear getting my roster filled out. That should level out some as I'll be activating and gearing far fewer characters in the next year. I also don't have strong enough squads to tackle all the higher challenge tiers in assault battles, but that feels more like would hurt the aurodium/electrium/zinbiddle stock. It makes sense there will be bottlenecks and tradeoff decisions to be made. I'm generally capping at R5 for those reasons. But it does seem a bit strange for carbonite to be my main bottleneck.