Not at all! A denial of penal substitution theology does not equal a denial of Christ's suffering.
What's the Orthodox theory instead of this, then?
The Orthodox "theory" is that it works because it works, and if one kind of language helps you draw closer to it, then more power to you.
To paraphrase C.S. Lewis a bit (and it was he who helped me to see that one can deny "penal substitutionary atonement" as an absolute reality and still affirm that Christ suffered and died for us), we have to be careful that we do not confuse the "thing" with the "explanation of the thing". He gives an example of eating supper: long before we developed our modern understanding of acids and proteins and minerals and such, people still ate their supper and benefited from it. Whether they understood how it worked or not, they still ate, and they still knew that it was good to eat. And it could be that our understanding of nutrition is flawed, and perhaps some day in the future we'll have a different explanation as to why eating supper is good for us. But that won't make our experience of eating supper any less significant, or any less real, or any less good.
It's the same with Christ. There are different ways of explaining why He did what He did, and why it benefits mankind. But whether we have the
exact understanding or not, it doesn't change our experience with that reality and make it any less good for us.
Another issue is that Who Christ is and what He has accomplished for us is something that is beyond the ability of human language to fully express. Although we speak and communicate ideas with speech, there are things, especially pertaining to God, that our language simply cannot fully express. Christ and our salvation are the same way. We can use human experiences and examples as means of describing what Christ did, but all those examples and models ultimately fall short. In other words, the best that we can do with human language is to make analogies
of this, but we will never be able to make a tautology
We find this all over the New Testament, especially in the Gospels (Christ makes use of a wide range of "atonement theories", so to speak). Christ uses the analogy of being lost and then being found; of being judged for a crime; of being sick and then being made well; of being on the wrong path and then finding the true path; etc. Paul and the other Apostles make use of a variety of analogies as well: being dead and being made alive; being in darkness and then coming into the light; being objects of wrath and then being made objects of mercy; etc. All of these analogies are different, and none of them are
the actual reality of our salvation.
So there really is not problem with the use of substitutionary language. That only becomes a problem when people try to make substitutionary language to be "the thing", as if it were the totality of the reality of our salvation. And because of all the baggage associated with that language and the layers of theology that are built upon it in many Protestant circles, we tend just to avoid the language altogether lest people think that we agree with all the "baggage" that is most often associated with that language.