They'll all need retouching in 3-5 years, and any reputable tattooer will tell you the same

Disagree. I've seen some done in that frame of time by people who know what they're doing, and they still look fine. If the artist did a shitty job plugging the color in or they didn't heal correctly, then yeah, they'll need retouching, same as everything else, which is what I meant by my statement about tattoo ink. The ink doesn't know what kind of tattoo you're doing, and as long as you have plenty of contrast and a good design, saturated the color well, and you use sunscreen, I don't see why a well-done watercolor tattoo couldn't last 10+ years. This is just my reasoning, and that said I still definitely wouldn't roll the dice and get one... but that doesn't mean they can't be made to last reasonably long.

No arguments from me about it being a fad, or the importance of quality equipment, or that traditional tattoos are predisposed to look good forever, and you seem to know what you're talking about so if you have any counterpoints I'd be open to hearing them.