I have never noticed Butter Cream having a bigger blackspot problem than other minis. There are some that are definitely far worse. Have you tried alternating your fungicides? Blackspot can build up immunity to a fungicide if you don't alternate them.

However, Butter Cream doesn't like our winters and always takes a bigger hit from winter and is slower to thrive in the spring. I'm hoping one of these years it will really take off and develop a plant to match the blooms, which are great.

I never noticed butter cream in winter with bigger hit. Next time i try to noticed.

I have two BCs in two locations at least 160 feet apart, so they don't pass it to one another. But they have had such bad blackspot that they are going to be put on the burn pile next spring. None of the roses next to them are that bad. They don't grow very well either.

Kentucky rose

If you are looking for a yellow mini to replace BC, I would suggest Breath Of Spring. It has stayed very clean in my garden in spite of the very wet spring we just had.

Breath of Spring