Were their tobaccos really that good or it just another case of unobtaninum makes people nuts?
A bit of both. I started getting into pipe smoking around ~2015 or so. I was still learning how to smoke a pipe and figuring out what I liked when McClelland closed down. I kick myself all the time for not buying any, but I was warned that English tobacco (like the popular Frog Morton series) and red Virginia (their most sought after stuff) wasn't for beginners and I should stay clear of any and blends like this, and that's basically what McClelland were known for. When they closed up shop, I didn't know anything about them other than tin art the the missus liked and always wanted me to buy it because of that. I never did, until years later when I could afford to pay 10 times the price for them. The more I think about how much Captain Black I was smoking back then and all the bulk aromatics I bought when I could have had McClelland just makes it worse.
But now I know a lot more about pipe smoking and the tobacco industry now. Some of the changes that happened, like the end of tobacco auctions and the end of tobacco subsidies that helped produce the "good stuff" ended. Not much is done "the old way" anymore, and the impression I get is that a lot of McClelland was done as close to "the old way" as possible, from the start of the tobacco on the farm to the end where they had their own proprietary process. At least that's the lore I buy into when I buy the occasional tin for an absurd price.
For me the proof is in the pudding though, as Frog Morton Cellar is one of the best tobacco's I've ever smoked. Frog Morton original (Frog on a Log) wasn't my favorite, but I'd never turn it down. I don't even believe this is due to the age on it, I think it's just that good. I have sampled 5100 and a few of the reds which were superb and I even liked some of their aromatics, even though many didn't. Many people hated Black and Lemon, which is one of my favorites from them. It really all comes down to taste. That being said, I did see a lot more people bad mouthing McClelland before the closure than I do nowadays. (EDIT: I especially saw a lot of "ew gross, what is this ketchup???" reactions to the now highly sought after Christmas Cheer)
There are still some "holy grail" tins that I look for from time to time when searching around for McClelland, but I imagine I'll find them in time. I have tried several match and alternative blends and while some stuff does check a lot of the boxes, none of them get close to the depth, sweetness, and smoothness that I've gotten out of some of these blends. It's a shame they closed, but I can understand their not wanting to compromise on quality. I feel like they were such a good team that they probably could have made some stellar tobaccos, even using subpar (or standard) leaf, but that's just my opinion. I understand that they were getting close to retirement age anyway, and have been doing it for longer than I've been alive, so I can understand why they'd want to enjoy the fruits of their labor.
TL;DR - Yes and yes.
