Couple clarifications:
1. Motorcycle engineers do indeed design the motorcycle geometry, suspension, and other design parameters around the tires. The tire profile, grip, tread pattern, are all evaluated and specified to work as a complete system within given performance parameters. Those that don't believe this simply do not understand how manufacturers design and make products. I do it for a living so I know the processes involved. It's generally a very complex and lengthy process where you have a set of engineering performance parameters you want to meet and have to pick and choose products made by others to meet the specs. The Me880 tires were selected specifically for this motorcycle because they are cost effective and offer the performance the engineers wanted. That's it. Nothing magical about it.
2. There is ZERO proof online that Metzler, or the ME880 specifically, are a poor quality tire or they are subject to so-called "cupping". These complaints are made by people based on perceived problems instead of actual measured evaluation to determine the root cause. There simply are too many variables to take into account to come up with a reasonable answer. Are your roads more rough than my roads? Do you have excessive luggage or extra weight that may cause excessive wear? Are tire pressures OK? You can not, with any amount of certainty, say the tires are the cause.
3. The manufacturer will perform a frame measurement test before assembly, however, the engineers always factor in build tolerances to the design and measurements so no two frames are going to be exactly the same. Factory built frames like the Rocket 3 will have some variance but it should be within factory specifications before leaving. My point is these variance can be fairly large which means a factory frame is NOT going to be perfectly straight and true.
4. A very small portion of the overall Triumph owners, and particularly the Rocket 3 owners, are on the internet. I would argue the vast majority of owners are very happy with their tires and don't experience issues like cupping. As with any car or motorcycle forum, you get the very small group of people shouting loudly that there is something wrong and others tend to believe it through word of mouth. Again, I've seen zero objective proof any Metlzer tires are bad or have problems. Prove to me the cupping or "uneven" tire wear is a direct result of the tire construction or design and I'd be willing to listen. Otherwise, all of this is just subjective noise intended to promote an idea that simply has not been proven correct.