I've seen a few sets of Michelin tires develop significant weather checking on vehicles that are parked outside. My dad had a set of Michelin Energy MXM4 tires on a car he bought about a year ago, they were 4 - 5 years old and significantly weather checked, and they were also quite hard and lacked grip.
I've got a friend with a set of LTX A/S tires on his Jeep (tires are about 3 years old), and they started showing noticeable (but not deep or worrying yet) weather checking on the sidewalls at about 2 years old. They're still soft and perform excellently though.
I've had good luck with Toyos and Firestones on my Jeep (sits outside) and my mom's Jeep (garage kept), between the 2 of us, we've yet to have a set show any cracking before it's worn out (never had a set last past 3 years though). I've seen 1 set of Toyos crack pretty badly, but it's on a rarely-driven car that sits outside, and they're pushing 10 years old, IIRC.
I've seen some Pirellis on other cars of unknown age, but somewhere in the 4 - 8 year range (one car sat outside, the other is garaged) that still looked brand new. The set on the outdoor car (P3000 Cinturato) was getting hard and losing grip, the set on the garaged car (P4000s) is about 1/2 worn and still surprisingly grippy (especially for being 205s under a 4000 lb car!).
The Goodyears on my dad's garage-kept Mustang (rarely driven) seem to hold up great. He had on crack a sidewall and start leaking while sitting when the tire was 7 - 8 years old. The current set on the rear of the car is 10 - 12 years old and not very grippy anymore (Goodyear Eagle VR60 gatorbacks), but the sidewalls look brand new, tires still drive smoothly, don't get hot when running at highway speed for hours on end, etc. The fronts are 3 - 5 year old Toyo Proxes TPTs, they still look brand new.