What Word Could I Use To Describe This Trend?

[serendipity04]

So, let's assume there's a trend where one thing was in its prime once but has sort of gone out of style but even then its popularity is still a bit more than half of what it was in its prime time when you quantify this "popularity". As English is not my mother tongue, my colleagues and I vaguely decided to use the term prime-low but I'm looking for better suggestions. Could anyone kindly help us out? Thank you.

[AZardoz]

- old-hat
- passé
- out of date

Probably not quite what you're looking for.
Try other social media, with a younger demographic. I'm sure you'll get the latest "in" expression. (just a lot of old farts here (-; )

[bednobs]

Conservative?

[ToraToraTora]

we'd say that it's popularity has waned.

[Jackdaw33]

Retro?

[brainiac]

Is he not banned?

[LeonBlank1995]

No longer zeitgeist. Great English word.

[davebro]

waning ?

[davebro]

What does waning mostly mean?
adjective. decreasing in strength, intensity, etc.: Many teens in focus groups expressed waning enthusiasm for social media. declining in power, importance, prosperity, etc.: The recent hacking of the retailer's credit card system will have devastating implications for its already waning business.

[dannyk13]

Passé

[bobbinwales]

Waned then flatlined and poised for an uptick. Bubbling under?

[bobbinwales]

No longer in but not out either

[andres]

Revived or Revival?