I think the lesser importance of good stats was very true in 1974 OD&D, where they didn't do much (Strength gives at most an xp bonus; no hit or damage bonuses, for example, and Dex gave at most a +1 to missile attacks, nothing else), but by 1975's Greyhawk we already saw Gygax trying to give Fighters a boost relative to Magic-Users, but only applying that boost to characters with Strength scores above 15, and ESPECIALLY ones with an 18. Same with the expanded benefits of Dex and Con, only applying to characters with decidedly above average stats.
There are two main ways to interpret this design, right? 1) the bonuses are meant to be rare, so treat it as a lucky occasion if you qualify for one, or 2) the bonuses are there to be used, and to (e.g.) make Fighters a bit better, so we're missing out if our characters don't have them. Gygax made a WHOLE CHART of benefits for Fighters with an 18 Strength; that seems kind of weird if only one in 216 characters ever use it, no?