You've raised a good point and I hadn't thought of it like that.
Yes, 8 years of sideways action is not good for investors, but it does show as you said, stability.

If we think that Ethereum is here for the VERY long term (at least the next 50 years) then 8 years of financial stability, but huge network growth (more and better projects being built)....
Then yes 8 years of sideways action can definitely be seen as a good thing.

Can it achieve the similar gains that Bitcoin has, in the 18 years it's taken to reach it's dizzying price point?
I think so.
(Wow! Bitcoin is going to be 20 years old, in a few short years!)