the only problem is, getting stuff from multi packs, which are prone to "failing" within 1-2y
My one major beef with Arctic is that the packaging for their 5-packs is extremely flimsy. Shipping damage, obvious or subtle, isn't uncommon. Of course, it makes perfect sense for Arctic to cut costs at the price points we're discussing, but still I think they do themselves and their customers a disservice. Investing an extra couple nickels on the box would go a long way.
Anyway, that sums up my experience: if the fans aren't damaged when you receive them, they will run happily for many many years--but you do have to inspect them carefully, particularly if they came in the 5-pack. You can reduce risk here by ordering your 5-pack of fans along with other items, so that they're packed together in a bigger box.
Honestly, the regular P12/P14 aren't particularly outstanding fans, they're simply decent fans at a ludicriously low price. As far as I'm aware there are no 5-packs for the CO variants, so you'd be paying 3x the price per fan which makes the CO variants decent performance at a slightly higher than average price, i.e. they're okay but not worthy of any particular recommendation. Let's face it, nobody would be giving the regular P12/P14 a second glance if they cost 3x what they currently do.
At first I thought I disagreed on the first statement, but it's a matter of perspective. By virtue of their unbeatable price/perf, Arctic fans have become sort of a de facto standard. This makes them boring in the same way that vanilla ice cream is widely considered boring. But vanilla ice cream is delicious. It's the standard because you can't go wrong. Most people like it just fine.
Purely in terms of performance metrics, Arctic fans compete favorably with even the most expensive and over-engineered items on the market. At reasonable noise levels, they'll give you 80-90% of the benefit of products that cost 7-8 times more. And they outright beat many fans at every price point in between.
But you're right; there's nothing especially exciting here. Fans as a whole category aren't exciting (unless you're a weirdo like me). Most people just want something that will move adequate amounts of air at barely audible noise levels, when the computer is at low load. If you know how to set a fan curve, almost any fan made by a reputable brand will achieve that goal. At high loads, things can get a little more interesting, but not that much more interesting; you're still probably best off limiting your case fans to a fraction of their max speed (my Arctic fans' curve tops out at ~1200 RPM). Heatsink fans merit more interest/attention, but again most people don't run at high (CPU) load often enough to care about fan noise in that context. And if we're talking gaming rigs, the GPU's noise level tends to set the tone, and almost no one uses aftermarket fans on their GPU anyway.
Performance at high speeds is basically a marketing gimmick, at least in the desktop market. As you suggested earlier, the Arctic Max is a good product because it has excellent performance characteristics at around 30% speed--and because it's cheap and reliable--not because it can move obscene amounts of air at 3,000 RPM. It'll sound like a woodchipper at that speed.
Every fan sounds like a woodchipper at that speed. This is another area where Arctic arguably did itself a disservice; the Max got a lot of hype when it released, in part because having the option to dial fan speeds up to absurd levels looks really cool on a performance chart, but when Joe Normie tosses a few Arctic Max into a machine running a default fan curve, he's likely to freak out at the noise level.
Fan tech is boring, in large part, because it's mature. There simply isn't headroom left to squeeze out substantial advantages at a remotely reasonable cost--and I do mean "remotely" reasonable; Noctua for example toyed with the idea of making the entire frame of their newest flagship fans out of liquid crystal polymer, but quickly discarded the notion due to cost. Even given that concession, the fans in question retail for ~$40. Part of me almost wishes they'd gone whole hog; it would be amusing to see how much better a $70 variant would perform, probably within margin of error.