Oddbean

"The neutrino particle was never hypothetical. It was made up to explain an observation." From wiki: "A hypothesis (pl.: hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it." Something made up to explain observations is literally the definition of a hypothesis.

You're correct. When I said "hypothetical", I really meant "speculative" or "conjectural". That definition of hypothetical is a bit broad, but ok, I'll take it. With that definition, every scientific model is hypothetical since it is proposed and requires continuous testing and validation. Nothing remains proven forever. Back to the original example: dark energy is a "hypothetical" scientific model, not conjectural. We are not waiting or looking to observe it, we already did measure it. It's a simplist shallow model, but the best one so far.

How independent is galaxy redshift from whatever phenomena produced the dark energy theory in the first place? Based on the wiki for Dark Energy, DE was theorized to explain supernova redshift In which case I am very skeptical that further redshift observations confirm anything positive about the nature of DE as an explanatory factor

DE is an integral part of the Standard Cosmology Model as a whole, without it it would fall apart. The LCDM together with the Friedman equations, explain most expansion measurements fairly well. https://en.m.wikipedia.org/wiki/Lambda-CDM_model