I read your blog post and while I am no ramen expert, it's not even close to my favorite soup, I think I have a few suggestions.
1. Your bones don't have a lot of meat on them. There is this weird misconception that bones make a good soup. It is in fact the meat that gives soups flavor, bones are mostly for the gelatin that gives the soup body. If you are feeling up for an experiment, try a chicken stock with chicken breast versus chicken carcasses. The former will have pure clean chicken flavor but almost no body, while the latter will be thick with gelatin and have a weaker, muddier flavor.
2. Pork broths need mad seasoning for reasons I don't understand before they taste like anything. Also whatever you are using for a tare is vital to ramen flavor, so I wouldn't panic if your broth is bland before you fully season it. I personally just use my chashu braising liquid (after marinating my eggs in it) because that stuff is amazing.
3. I am a bit surprised that you browned your chashu first and then did a relatively dry braise. Chashu is mostly about texture for me and both of things seem like an impediment to tenderness.
I didn't see your final broth. To me what makes ramen interesting is that emulsification of fat and gelatin and not necessarily the flavor. Did you get that milky consistency associated with a good ramen?
A lot of this is down to personal preference, so I would work on how you want ramen to taste. Some people might want it to taste mostly of miso and tahini, you seem to want a pork broth. If that is true I would definitely spring for a meatier cut and just barely cover with water.