Everyone's mileage may vary, of course, but I thought this snippet worth pushing back on. On several levels. First, I think your 20/80 categorization is too simplistc. Second, for me, I'd say you have your values reversed.
I kind of look at thing in tiers. By your reckoning 20% of a 26/22/24 episode season yields 4-5 classics (Trek at it's best) per season. I think, on average, that is in the ballpark. Though I must say, some of the best Trek seasons (TOS1, TNG 3-5, DS9 4-6, VOY4, ENT4) are gonna come in significantly over, while some others will come in under.
But my bigger issue is with the other 80%. For me, while I'll admit there are cringeworthy moments from time to time, and some clunker episodes (Tom & Harry in the holodeck, again), I enjoy the non-classic episodes just fine. "Sub Rosa", "The Outrageous Okona", and "Code of Honor" bother me not one iota (though great episodes they are not, well below average). And I enjoy most average episodes a lot.