Hiya!
Simply put... I think this is all based on individual experience and play style.
In my 5e game of Genericka, for example, I've had three clerics, a druid, two warlocks and two sorcerers (iirc) (and maybe one "Fey" Paladin...for a single session? Maybe?). After that, everyone else were of the "Martial type" character classes. This is for over 6 years of play. Nobody playing any of the Martial classes
ever felt "weaker" or "less effective" or that they had "less things to do outside of combat".
The reason, I think, is simple: I'm an Old School DM. I don't "build encounters/adventures" to suit my Player's Characters other than the
absolute minimum (e.g., "Ok, 5 PC's, about level 3"; I don't care what races they, what alignments they have, what backgrounds they have, or what classes they are...and neither does my world). Because of this, there is a very distinct "flavour" to the whole game that simply involves all of the "3 Pillars". Averaged out, I'd say about 40% Combat, 30% RP and 30% Explore. Because of this, PC's are usually doing "stuff" that
any PC can do.
Next would be that our 'style' of play is more along the line of "What would make sense for my Character to do?", and not so much "What would make sense for ME to do?". It's the equivalent of a PC caster with only 1 spell left saying "We need to press on. We don't have time to sleep right now...he's going to get away if we do, and who knows what he'll do during those 8 hours!", versus "We need to do a long rest to get spells back. Then we can cast Spells XYZ and ABC to pick up his trail; we can then deal with anything he did because we'll be at full strength". The first is purely "RP and narrative driven from a Characters perspective". The second is purely from the perspective of "We will have these mechanical things available".
Combine those things... my Old School Style DM'ing where I
do not "build to the PC's" and with the Players thinking as their PC's, not as Players trying to "mechanically optimize for success", and you have Fighters being every bit as 'viable' out of combat as anyone else...and being a bit MORE viable throughout the adventuring day (because a Fighter never runs out of attacks). If I was to "build to the PC's" and I DM'ed with the assumption that the PC's were "heroes and supposed to win"...then I'd agree, and the "mechanical based decisions" would make more sense; because the Players would know that the bad guy would 'pause' his bad-guy plans as the PC's rested for a day. Or at least, nothing REALLY bad would happen...because "that would be unfair to the Players". Hogwash to that I say! If the Bad Guy needs 4 hours to unleash the Undead Plague Vial into the towns water supply, and the PC's decide to take a long rest before they confront him...well...that's bad news bugbears to that poor town!
And yes, before you ask... No, the Players do not need to know they have a 4 hour 'time limit'. That's the ENTIRE POINT of why my players would likely decide to push on, despite lack of spells/abilities; because they KNOW that the world/adventure isn't "built around them"...ergo, they wouldn't take the risk.
Wow. That was a long way to say: "I disagree. I think the usefulness of any Class is primarily based on the DM's style".
^_^
Paul L. Ming