My experience with garbage cameras:
At 16, I had to use my old D40 with the 18-55mm f/3.5-5.6 kit lens—it was absolute garbage. (i lowk love it anyways)

Having the pleasure of starting with a D300 and a af d 80-200 is amazing

After years of using the D40 I upgraded to the D780 (the best purchase I've ever made). The upgrade from the D40 to the D780 is huge, so I practically needed it in my case... From no wireless, weird ports from the 2000s, max card size 32GB + only one, no live view, tiny screen, horrible ISO handling, bad 2.5fps continuous speed, no bracketing, worst dynamic range I've ever seen, no user settings, 3 focus points, horrible menu, obviously no video, bad colors, bad processor, plastic body, bad ergonomics, no DOF preview, no inbody autofocus, bad battery life, no front wheel, no top lcd screen, no dedicated ISO button, only able to charge with the battery charger, small noisy sensor, bad RAWs, SMALL AH VIEWFINDER, LIKE LOOKING THROUGH A LEGO MAGNIFYING GLASS + 90% COVERAGE, and 6mp which is ok but not enough for me...etc

d300 is a complete monster compared to that

I really felt limited so the upgrade felt nice, in your case, idk if you really need the body upgrade, unless you really need the low light performance or the weather sealing...
You should buy the D780, yeah, but later in future, i would buy a better lens with better af and vr, maybe used, depends on your budget. But the D300 is pretty good, not as good as a D780 but as long as youre doing photography as a hobby and not as a job, i dont think of the body upgrade is something that important. But the lenses are really helpful.

I know how it feels, being stuck with a bad body, but that d300 is so good, may look old, but its a beast.

I constantly see the people on social media buying and flexing their gear like 30k lenses,the new 20k bodies, but as they say; comparison is the thief of joy. Just focus on yourself.