Correct, they don't automatically make you hit more homers because you've become bigger & stronger, although they can. To me, the records are tainted because someone like McGwire took them for so long that he - and he admits this is why he did it - ended up playing in considerably more games, which pads the numbers he would have had otherwise. Nine innings instead of seven, 150 games instead of 130, etc. That adds up over the course of ten years.
By his own admission, he was ready to retire a few years earlier because he was taking too long to get over injuries. He decides instead to juice and ends up playing a few more seasons. That's an awful lot of homers that figure into his total of 583.
Add to that the fact that by being in more games, he had more RBIs - those are runs that may have been game changers for the Cards. He altered his personal records, as well as the possible outcome & standings of other teams - both the Cards and team in other divisions. Particularly if a team is only one or two games back at the end of the season.
Whether he's doing it out of ignorance or denial, his explanation that the only thing the juice altered was his personal health is incorrect.