I don't really see this as "cheesing", so to speak, simply because he's not taking advantage of an exploit to avoid death. He's incurring decent hits, but with high, high damage reduction. And although getting all the required items may take some work, it isn't exactly beyond what the developers had intended. Items like the Frozen Turtle Shell are in the game for a reason, and that accessory received a tremendous buff for a reason (seriously, the change is phenomenal).
He operated within the game's limits and the developers intentions, without the use of a mechanic that overrides damage or negates it.
If anything, they'd weaken the beetle armor to be more in line with Solar Flare Armor (since it beats Solar armor in damage reduction anyway, which makes no sense to me), OR weaken the Frozen Turtle Shell (less damage reduction or multiplicative versus additive), or allow the Moon Lord to apply an Ichor debuff, or EVERYTHING I just mentioned.