What did you use for closed loop guidance? If you aren't aware of it NASA has a lovely paper called UPFG "Unified Powered Flight Guidance" [1] used for the space shuttle. This was implemented and made more universal for KSP (of course) by Przemysław "Noiredd" Dolata as PEGAS "Powered Explicit Guidance Ascent System" [2]
If it's your thing you could try implementing it and getting a single continuous burn to final orbit.
For this model I kinda just made up my own system to play around with it, while it wasn't very effective it was pretty fun. That being said thanks a lot for the recommendations, I wasn't very aware of the options I had for it.
If it's your thing you could try implementing it and getting a single continuous burn to final orbit.
Awesome work BTW!
[1] https://ntrs.nasa.gov/citations/19740004402
[2] https://github.com/Noiredd/PEGAS
Edit: I now see it's on your roadmap, so I guess it is your thing.