Under articulating penal substitution is not that same thing as out and out denying it. One of the things we should consider is how some of the church fathers actual handle scripture not merely the systematic treatises they do (or do not) write, especially since the impetus for lengthier treatments was often combating a particular error.
Consider this from Chrysostom:
On 2 Cor. 5:21 "God allowed his Son to suffer as if a condemned sinner, so that we might be delivered from the penalty of our sins. This is God's righteousness, that we are not justified by works (for then they would have to be perfect, which is impossible), but by grace, in which case all our sin is removed."On Gal. 3:13 "For the people were liable to punishment since they had not fulfilled the whole law. Christ satisfied a different curse: the one that says 'Cursed is everyone who hangs on a tree.' Both the one who is hanged and the one who transgresses the law are accursed. Christ, who was going to lift that curse, could not properly be made liable to it yet had to receive a curse. He received the curse instead of being liable to it and through this lifted the curse. Just as, when someone is condemned to death, another innocent person who chooses to die for him releases him from that punishment, so Christ did also...Just as by dying he snatched from death those who were going to die, so also when he suffered the curse he released them from the curse."
This is not to say that Chrysostom had a fully articulated or full blown view of penal substitution as it was later come to be understood. But his handling of Scripture is quite carefully and at least in these quotes he understands a central aspect of the atonement and Christ's death for our sins.