I've had multiple Marathon Supreme tires succumbed to gashes. I don't consider them a touring tire. More like a commuting tire at best.
Same here. Used them touring and commutng but not what I’d pick where sidewall durability was needed. One thing I noticed on the 35x700 size was that if the psi was low there was a squirm in handling different than other tires when psi was low. Also sidewalls started to go before treadwear required replacement.