The result of the shedding was deplorable.
the test strip had a nice flow
Sorry, what do you mean by 'shedding' and 'flow'?
Can you post some pictures of the test strips/sheets you've made, with a brief description how you exposed and processed each of them?
What kind of paper are you using? Assuming it's variable contrast paper, are you using any contrast filter, or just plain white light?
Now I'm sad that my developer has lost strength
Have you tried developing much longer? Paper development goes to completion, which basically means that you develop until nothing happens anymore. The time this takes, depends on a couple of factors. With very old or dilute developer that has lost strength, the development times suggested by the manufacturer may not be sufficient anymore. You may have to mix it less dilute, and/or extend development time (sometimes quite a lot, too) - if you're fortunate enough to get full development in the first place.
Note also that there's a relationship between exposure, development and contrast. Assume that you're not developing to completion, and that development is actually cut short long before it's really done (e.g. because your developer is too old). In this case, if you give more exposure, you may still get good overall density (somewhat decent blacks in the shadows). But contrast will be low. Conversely, if you give less exposure, you end up with an overall pale/low-density print. It's sort of comparable to printing at a low contrast grade, with the exception that you're never going to get really good black/dmax if you under-develop the paper.
it turns out to be 4 years old
Was the developer bottle opened before, or was this a factory-sealed bottle that you recently opened?
You can remove a factor of uncertainty by using fresh chemistry.