Yes, I also feel like most of the off-the-shelf models struggle with generating nice and natural looking logos, especially something that resembles vector graphics.
Since you have been fine-tuning the models yourself, I really think the tool I mentioned could be useful for you. The one I linked just obviously only lets you queue up one pair at a time, however, we also have an API that lets you get responses on 100s or 1000s of pairs quickly. Please feel free to reach out if you want to try it out. My email is on my profile.
The version we currently have open is only 2, but we are soon going to release a version that is more general ranking which can do 3 and more options. Hit me up and I can keep you updated when it is available!