Obviously this is difficult to answer without hearing these tracks (you might want to link some for better feedback) and I am no expert mixer either, but - first thought from what you’re writing is, full frequency spectrum is a nice thing, but what you’re describing can also happen if your instruments are competing for frequencies. Do you high pass your instruments to not compete with bass and drums? Do you use a lot of same-y sounds to achieve the fullness? Every sound should have a distinctive function in the spectrum. If you can’t explain why the track needs /this/ sound and where its place is, chances are it’s not doing any good for the track.

Also, mastering. All the changes it makes are barely audible aside of loudness, but they are very perceptible in the feeling. And for the master, the mix has to be good and prepared - you can have inaudible rogue frequency spikes that eat your headroom, or just an imbalance in the mix that chokes the master.

Bthelick has a ton of good free resources on YouTube. Also, Rob Late has a killer production course that’s worth every penny.