IME, "mercenary adventurers who are recognized as such" and "campaign that covers a significant part of the level range" seldom go together.

There've been plenty of (usually shorter) games where we're hired / mercenaries, which usually don't involve changing level much - we've been everything from "disreputable vagabonds the baron offered a few coins to investigate the cursed ruin because we're disposable" to "elite agents personally sought out by a demon lord and offered unique payments to facilitate an Abyssal coup", but not in the same campaign.

Meanwhile there have been campaigns with a significant power curve over the course of play, but we weren't generally mercenaries in those, rather people who either have a genuine allegiance to a nation / organization, or who just get caught up in major events by being in the right place at the wrong time. And not people who were in-setting known as "adventurers".

So it avoids the issue that the way society relates to "skilled mercenaries, but nothing superhuman" is going to be substantially different than how they relate to "potential one-man army" types.