All Biblical typology is self-contained to the Bible. There is no such thing as extra-Biblical, Biblical typologies. So, anything extra-Biblical automatically becomes "private interpretation".
Additionally, a poor understanding of Biblical typology ends up engendering "private" interpretations. An example is above, in your quote.
You wrote that Paul makes use of
Isaiah 28:11-12 to give us a picture of Holy Spirit baptism. That's not true. Paul makes use of
Isaiah 28:11-12 to bolster his teaching on the particular charismata "diverse kinds of tongues". When God uses someone to speak in a diverse tongue, it is just as Isaiah wrote, that God is speaking to people. Further, Paul goes on to explain that "tongues are a sign...for them that believe not..." that is, for unbelievers.
In
Isaiah 28, God was sending the Assyrians upon Israel as a judgment for their sins. These warriors from far away spoke with other tongues, that is, with languages the people of Israel did not comprehend. The people of Israel were being judged by God as "unbelievers" in Him, and the sign to them that God was giving them was that men of other tongues were going to speak to them, but in reality, it was God doing the talking.
So, when an unbeliever hears someone speak with another (an-other) tongue, with God being the one really doing the speaking, it is the rest and the refreshing, but the people, the unbelievers will not hear. So what then does Isaiah say regarding the Word of the Lord? It is given to Israel in small increments (like a "stammering tongue" can only speak in small increments of sound), as a means whereby Israel might "go, and fall backward, and be broken, and snared, and taken" (
Isaiah 28:13).
Similarly, when the unbeliever hears God speak to them through a diverse tongue charismata, it is a sign to them that people of a strange tongue (like the Assyrians and Israel) are going to sit in judgment against them for resisting the rest and refreshing that could have been theirs had they not remained in unbelief.
So, because you have not correctly grasped the typology, you erred in your understanding of how Paul applied the verse from Isaiah, incorrectly therefore assuming that Paul took the verse out of context to make it say something it did not, when it fact, it reads exactly as Paul indicated, and fulfilled the exact same purpose for when it was originally written, thus completely preserving the context of Isaiah while making use of it in
1 Corinthians 14.