Context matters.

Traditionally, "Of Counsel" was/is used for a relatively experienced lawyer (ie more senior than a senior assoc) who's not on the partnership track or has no expectations to be made an equity partner. These guys are pretty doing their own thing, and it's much easier for them to pack up their practice and move elsewhere. Similar to "Consultant" but Consultant title is usually for super-senior & respected practitioners (very experienced semi-retiring lawyers, former Judges or legal service, etc).

Nowadays the title is used & abused for all sorts of purposes.

Some firms like A&G now use "Counsel" as a rank before junior (salaried) partner. In order to stretch out the rungs.

Some other firms like Providence, simply call all their assoc-level lawyers, "Counsel" which sounds like title inflation to me.