"A Quick One" was kind of a partial concept album-- a concept suite, maybe. PT didn't have enough additional material to make it longer and as you noted they already had the album mostly done.
(Of course you remember also that PT originally envisioned "Who's Next" as a full fledged concept album -- the Lifehouse project -- but kind of fell apart on the whole thematic "concept" and opted instead just for an old-style song collection.)
In a way, Sgt. Pepper is about half a concept album: SPLHCB and "A Little Help From My Friends" on side one, with "Good Morning," SPLHCB Reprise and "A Day In The Life" to close, with the other seven songs just dropped in at random.