At that height, even by 1990’s standards with long stems, you should be on a large size MTB, which would have been a 19" to 21" sized bike back in the day (seat tube measurement).
These day’s you would most certainly be on something with a reach around 460-470mm.
Geo between road and MTB is not comparable as the bikes are too different these days, eg my TCR has a reach of 400mm (and feels good with a 80mm stem)…my smallest MTB reach is 430mm (which feels small), and the average of my other 4 bikes is 455mm (which feels perfect) with 40mm and 50mm stems.
I am 5’10" / 178cm.
If you feel scrunched up on the Kona, and you’re thinking of a longer stem to compensate, then I hope you have a good dentist as s/he might be needed from all the OTB’s you might experience!
I would agree with most of the above people that the frame is just too small for you.
The other thing to take note of in MTB fit, is that the key is to be sitting more central to the bike than what you do on the road. This is for when you are standing and moving around, which you will do well over 50% of the time (or you should be if you’re riding anything above a beginners trail or a fire road).
Just take it as a sign that you need a new bike…the universe has a way of telling you these things…