My impression, having started watching the game in 1971, was that we were really struggling to find good batsmen. Boycott and Edrich were exceptions, but seemed quite old to me even then. The lack of younger batsmen coming through was really shown by the line-up in the 1972 Ashes when the average age of the top 5 must have been around 35, or maybe even higher. And it's not as if they were scoring many runs, either. For a while, newcomers didn't do much better - Lewis, Denness, Roope and Jameson were all tried and found wanting. Fletcher came and went quite regularly, maintaining a decent average by filling his boots against the weaker sides but no-where to be seen against anyone challenging.
Pre-Gower, the only ones who showed promise were Steele (see the 'Shafted' thread), Woolmer and, for a brief while, Randall. Woolmer's test career, after making 3 Ashes tons, never recovered after joining WSC. Possibly the best captain we never had, judging by his subsequent career. Randall's career nose-dived after that run-out by Boycott, but it's easily forgotten how good he looked for a brief three-test period in 1977.
For whatever reason, we stopped producing great batsmen by the early 1960's. Cowdrey, May, Graveney and Barrington had all emerged by then, as had Boycott & Edrich, albeit only just at that stage. I honestly have no idea why.
EDIT
Just realised that I had forgotten Dennis Amiss, who really was terrific until committing the apparently unique crime of being undone by Lillee and Thomson