@Hemophiliac Interesting. Maybe I was using the wrong approach due to how I learned mixing mainly through YouTube. Tutorials hardly use orchestra music for demonstration, so the way "mud" develops (e.g. overlap from untuned percussion, resonances from recording etc.) and is handled is very different.
I was actually already considering the intervals, but rather based on instruments and sections. For example close writing in the flutes is fine but for trombones open writing is better. The goal is of course to avoid smearing the sound from a musical point of view but so far I hadn't considered this in the context of mixing. In hindsight it is of course obvious, but in my head composing and mixing were two separate and independent stages with independent problems.
That is also why increasing the reverb just worked. The writing was already clean with regards to intervals, resonances were fixed before the reverb and recording issues can't be present due to the instruments being modeled.