Hmm, I actually never looked at it that way. I will take another look at your interpretation though, quite interesting. I always interpreted
"gates of hell shall not prevail against it" in the context of my understanding/belief of the first part of the verse and the revelation that the Father had given Peter. My interpretation of the first part of the verse is:
Christ built His Church upon the divine revelation/understanding of the Truths of God/Word of God, just as had been revealed to Peter by the Father, as mentioned in verse 17, which was the Rock that Christ spoke of, being the foundation later spoken of in the NT. With Christ being the Chief Cornerstone (Christ being the focus, center, most essential component) of that revelation/understanding according to Ephesians 2:19-22 in both the capacity of who our preaching points to, as well as Him being the chief layer, with the apostles and prophets, of the foundation of the Church. Again, that "understanding/foundation/Rock" being the Word of God and true preaching of it, pointing to the Living Word, being Christ and His redeeming Blood.
For the second half of the verse,
gates of hell shall not prevail against it, I interpreted that to mean that no power of the enemy could ever stop salvation and the Church going on unto perfection. I used to hear the older folks around here say, "no matter how hell or high water comes my way, I'm going to still move on." I think that is a modern way of saying
"the gates of hell shall not prevail."
I think in some way our interpretations intersect with regards to salvation... But I may not have explained my interpretation of the verse well enough and may seem to be way out in left field

Just let me know

But I'm gonna study your thoughts as well, thanks!