I've been in a similar situation where I got deceived by my bedroom in terms of sound production.
I mean the sound being cool while in the bedroom and sounding a different way while outside.
That's why I would say room treatment matters a lot when it comes to getting a good sound quality. It does not mean that you have to spend a lot to achieve that.
You can get a couple of acoustic panels that are quite affordable, fixed in some corners, and behind the monitors.
That's not comparable to getting new gears, but it can improve the sound quality.
I can only say you go for upgrades on the music equipment if you've not got a good monitor or decent headphones. However, if you've got them, then I think doing a simple room treatment is the first step for me.