Why is my stock flavorless?

Couple notes or suggestions;

1. Added in fat? Typically for ramen adding in a copious amount of finely chopped pork fat is a must. Usually boil a slab on top of bones for 4 hours and then chop and add. Serve with a side of lipitor.

2. Where is the savory flavour or unami? You need to either cook some veggies/aromatics to get the Maillard reaction or cheat and add some MSG and/or a unami super boost (mushroom, marmite, anchoivies or other). Lots of techniques to get savory flavour; which I think is what you may be missing. soy sauce, or miso are also classic; pending what your end ramen is going to be.

Overall the technique is good; just missing the flavoring step; the base broth itself is not going to have a lot of flavour since you are not roasting; along with blanching step.

Blanching for a clear broth does remove a significant amount of flavour; but is more classical ramen approach.

Another trick you can use to extract more flavour is add a acid early to process; 1TBsp to 1/3cup or so of apple cider vinegar. My goto when making a thai sour chicken soup or some other white broth soup that will be loaded with lime and cilantro later. Drastic flavour change; so be-careful and test first.

I've always made stock using meaty bones with salt added. I have borderline low BP and can use the sodium. But I've heard many people making perfectly good stock without salt so I don't think that in itself is the problem.

If others agree your stock lacks flavour, it won't be due to your method. I'd say it's more likely your meat. Remember that chickens are slaughtered at a very young age - a matter of weeks - so the chicken backs would be from young chicken. Older larger chickens would be left whole for roasting. The same goes for pork hocks. A grown pig is a very large animal and you'd be able to judge from the size of hocks you used, the pig they came from wasn't that old either. Most pork we eat comes from pigs between 5-10 months of age - no longer babies but comparable to roughly a young teenager.

Old hens and parts from fully mature pigs was what was traditionally used to make stews and soups. The meat was too tough to fry or roast but was very flavourful for slow simmering. Think of the difference in flavour between veal (calf) and beef.

I make stocks on a weekly basis and am used to some variation in flavour but the lack of potency usually comes from 1) too much water 2) not enough salt

Now I don't use salt in making the broth but it's often the salt that draws out the stock's flavour and so the final broth is often much richer when you salt or add soy sauce, fish sauce etc. My method these days involves a pressure cooker with a fixed volume of liquid - not necessarily covering the meat. My favourite ramen broth is a smoked ham hock with 1L water in the pressure cooker for 45 mins and it's fairly intense without extra salt.

Too much water? not reduced enough ?

I would color the meat and the vegetables with a little bit of oil (one batch for the meat and one batch for the vegetables) before adding the water.

I have found triple reducing helps optimize flavour and viscosity. Reduce, add water 3/4 of original amount, reduce to desired outcome. I also love salt more than most so to avoid over salting I finish with a splash of vinegar. White, rice, apple, or whichever suites your preference for the final profile.