Up until the 60s or 70s that was pretty much the norm. Every club had a first team, and the reserve RB, LB, left half, inside right or whatever came in if the first teamer was injured. Occasionally a reserve would force their way into the first team if the player in possession went off his form. There was no such thing as squad rotation.
You forget they were only allowed one substitute obviously given that you wont be playing as many players.