I saw Rush in 1981 or 82, and seen many vids of him over the years, and I honestly can't remember ever seeing him use one finger until more recent times. But I have no problem taking you at your word. However, Geddy also has zero problem using a very solid two-finger technique when he needs to. I've seen him do it plenty.
As for technique not being agreed upon, yes, people are developing new techniques to this day. Pick, pick and fingers, three fingers, thumb and three fingers, and thumb and four finger techniques are being used, and that is good. Technique is not a static thing. But the more techniques you have at your disposal, the fewer limitations you will have. That is a fact that can't be argued. Yeah, Jamerson only used one finger. Yeah, Geddy sometimes uses one finger. But the points that are always lost when people bring up famous players and their techniques or lack of them are:
1. People who ask questions like our OP are looking to overcome their limitations.
2. You ain't Jamerson or Geddy.
Well what we're talking about here is the idea of whether there is something called "bad technique" or the right or wrong way to play the EB. Not necessarily the mere fact that different techniques exist; that's very true, but it's not really the question.
My position, again, is that the ROI of this or that technique is the better way to think about it than whether it falls into "good" or "bad" technique. Having multiple techniques available to get your job done actually has a questionable ROI. The time and effort spent learning techniques that you might never use, or that don't materially impact how you play and sound with the music you enjoy playing (or are paid to play), might actually be a waste of time.
For example, if the gig is a genre like Motown or something like Austin TX blues, it wouldn't make sense to spend 6 months mastering a 3 finger plucking technique to prep for the gig instead of practicing the set list with your existing 2 finger or even 1 finger technique. That's an ROI evaluation - not a "good" or "bad" technique or habit label - where ending up with _fewer_ "tools in the toolbox" will lead to a _better_ outcome at the gig.
To take another example, there are similar arguments out there about the fretless bass and whether it makes you a "better player" or encourages "better technique". I spent the last 20 years on the FL exclusively and I still often ask myself this very question: Truth is the ROI on the work I've done is a mixed bag. I originally went to the FL because I couldn't make a fretted bass sound good. But it turns out that I can't make the FL sound good either. I suck about equally bad on both; it was too late in the game when I figured that out, so I've just stuck with the FL regardless because it's now what I'm used to.
One possible benefit is that the FL is much less forgiving than the fretted bass when you don't know the notes. On the fretted bass, you can kind of flail around making guesses and it'll forgive you if you flub just enough to fret the note and pluck it at the same time. On the FL, the same level of mistake sounds like a dying cow. So I'd say it's made me more attentive to being a "note-based player" (in the sense of Jeff Berlin) and making sure I've practiced what I intend to play more thoroughly than I might have otherwise on the fretted bass.
Truth is, that's kind of all I can think of as far as the bennies (for me) of 20 years on the FL. The ROI on the FL is questionable unless a hypothetical gig might require what the FL offers over the fretted bass. That's apart from fact that I really enjoy the challenge. Yes's "Tempus Fugit" is a real task to play on my tony franklin vs playing it on a 4003 like I used to, and for some strange reason, I get a charge out of working on it on an unlined fingerboard. I guess that's a benefit too, but on a gig, I'm much more likely to drag a fretted bass to the club if that song is on the set list.
Again my position is that the gig drives the tools you use and the sound and whether something is a good or a bad habit. Not the other way around. We learn the techniques that enable us to play what we want to play the best we can play it. If it's a question of improving the way you do that, than certainly you can say a better way is "a good habit" over a "bad habit". But if it doesn't further how good you'll be at the gig (or increase your enjoyment of the music you prefer), than it's hard to apply those labels to what you do now vs another way of doing the same thing....
L