We can't hear your tracks, so you need to search the forum for how to post them correctly or stick them soundcloud or something.
It shouldn't be too difficult to get a solo piano type track to sound good. There's 2 ways you can probably tackle it.
1. The long road. If you can't hear it then you can't mix it so it may be that you need ear training , a better monitor system, mix room treatment etc. Then once you can hear it you need to learn what sounds good and what doesn't and know how to adjust it which comes from experience. I can wholeheartedly reccomend 'Mixing Secrets For the Small Studio ' by Mike Senior as a book that will systematically teach you to produce better mixes ( with audio examples provided online ) and I'm sure there are courses that might better fit your learning style if books are not your thing.
Try this to train yourself to hear EQ
https://www.soundgym.co/playground/eq
2. The quick and easy path to the dark side. Plugins and AI have come a long way and there are some great tools now that can do the heavy lifting for you so you don't have to be a great mixer / engineer necessarily to acheive broadcast quality but it will probably cost you more to buy these tools than learning the hard way although it might well get you over bar much sooner. The good news is you can trial a lot of these things and see how you go. Here is my quick and easy plugin list.
Metric AB - To get in the ballpark you must really A/B your stuff with the references. Plugins like this will show you pretty quickly if you are loud enough/ bright enough etc. compared to the Ref tracks
Gulfoss - This is like an auto EQ that changes 1,000 times per second but it great for brightening a dull mix without sounding fatiguing and harsh. You can use on individual tracks or a whole mix. i think there is a Black Friday Deal too but there is a trial too.
Soothe - This is brilliant for taming harsh resonances which there can be a lot of in piano sounds. Most things sound better with it on ! Very easy to use.
Pro-Q3 - This is a fantastically flexible EQ and has some great features but one of the super useful things it can do is a better version of EQ matching because you can vary the amount of the EQ curve it applies so if you feel your mix isn't quite getting there try it and apply like 30% Eq match and this often makes a noticable difference without overdoing it . Plus you can make each band dynamic so it's not doing it all the time, just when it needs to.
StageOne - Fantastic for adding " soundstage " to work mix, just stick it on , find a preset, tweak to taste. Instant front to back depth and wideness
Ozone 9 you already have, and it sounds like it's helping but the Tonal balance Control is invaluable to visually see where the issues are in your mix, so if they are telling you it's too dull you should probably see that on the Tonal Balance Control curve.
So that's the fast and easy but more expensive way.
My other main tip is to make sure if you set up a send return for your reverb that you're EQ-ing the return mostly by high pass filtering all the mud out of it..maybe 200-300hz sort of range and then find the most prominiment frequency of your mix, say 3k for arguments sake on a solo piano and make a cut in the reverb return EQ so that the most audible part of the mix isn't smotherd by the reverb.
Hope that helps ! I
Mark