No one chooses to fly in moderate or svr turbulence. So it's often a situation that you just have to deal with the best you can.
Is OPT ALT acceptable for the overwhelming majority of the flying we experience? Based on my experience the answer is yes.
Do I restrict cruise to fly around 2000-4000' below OPT ALT for typical weather? No. Thunderstorms? No.
Are cruise levels restriced for turbulence? All the time. Happened on both of my last two trips. In radar contact it's easy enough to get Pireps or be the weather ship yourself if no one else has checked it out.
Last trip we checked with ATC and we could out climb it. Reported FL280-360. Instead of flying 11,000' below OPT ALT(FL260) we flew 1000' above OPT ALT(FL380) in smooth air. Would we have stayed there in moderate turbulence? No, we'd have flown at FL260 in smooth air.
Non-radar? You have to be a lot more cautious. Pireps of mod-svr turbulence along our flight path while non-radar (overwater). Dispatch figured we could be 1000' above the turbulence if we were willing to fly 1000' below MAX ALT. Four pilots, 60,000+ hrs experience, and none of us thought that was a good plan while non-radar. Dispatch with zero heavy jet experience was surprised that we choose to fly across the pond in the upper 20's _I'll have to upload another 10,000 lbs of fuel." Four pilots looking at speaker (SATCOM) thinking the same thing - yeah, so what!?!? Sometimes caution is warranted.
Two to four thousand below OPT ALT as a technique? IMO overkill.