First time superman vs shazam,superman wins,but not because he have more stronger,faster,more powerful,it's just because..eh...
Shazam is really powerful charater,he strength is no limit,infinite speed,and Absolute invulnerability,you cant hurt him,oh,superman hurt him is because shazam become weakerin superman universe,lol
So,if shazam vs superman,back silver age,both was absolute invulnerability,they are cant hurt each other,like this
I know that was sounds crazy,but if a bronze age superman(who isnt absolute invulnerability) can withstand big bang(BA superman and superman-prime)a silver age superman would be withstand more,if it's true absolute invulnerability
Both equal to strength,(I post some shazam feats)and as fast as PC superman(beyond infinite)and even both have same PIS power
The only way superman can beat shazam,it's just because DC dont want to superman lose,they are depowered capation marvel,well,we know this is pretty selfish