Today's game is so different, teams usually have 8 relief pitchers and a guy that only pitches the 9th, 8th,etc. A complete game is almost impossible, there probably hasn't been this season ? How many last year, maybe 10 ?
In the old days a starter was expected to go the full 9 innings and also hit before the dh existed, sometimes a guy would pitch both games of a double header and they pitched every 4th day, not 5th.
Now you need an opener and the starter has done his job by going 5 innings, maybe 6 on a good day.
Even in the 70's a complete game wasn't a rarity. Teams almost always use 13 of 25 roster spots on pitchers, leaving a 3 man bench
A 2nd catcher that really can't be used
An infielder/ utility man to cover any infield spot
And a 4th outfielder that might also be capable of playing 1B in a pinch
Why not just up the roster limit to 30 ? The player's union would like that. It would pass easily, shorten the season a little bit also