The arrangement point is the one that separates people who improve from people who buy things.
Practical version: mute everything and bring parts back one at a time, and ask what each is doing that another part is not. Most amateur mixes have three things playing the same role in the same range, and every one of them is fighting.
The fix is usually not processing, it is playing less. That costs nothing and it is why the same song sounds better after somebody removes two parts.