Machines for actual racing on have always been built in particular ways and at any one time (or even over time) there hasn't been too much variation in them; more details rather than fundamentals would be varied. If someone with enthusiasm and potential rode a few club time trials on a clearly unsuitable machine, often it would be pointed out to them that they would go a fair bit quicker on a different bike. Often better wheels (i.e. not with 35mm tyres and wide rims...) would come first and any benefits (for racing) would be fairly clear.
However maybe thirty years ago folk used to turn up on certain winter training runs locally (which normally attracted members from several local clubs) with all kinds of bikes, varying from one-time racing machines with mudguards nailed on somehow, through to various grotty heaps which had been touring bikes in a former life, even cx bikes or MTBs with slick tyres. No-one really cared what bike you rode as long as it didn't break too often, didn't shower everyone else with crud, and was ridden safely enough so that wheels could be followed. Some runs were carried out in darkness, so lights were obligatory. Fixed gears, hub gears, 1x, 2x, 3x derailleurs, side pull brakes, hub brakes, centre pull brakes, cantis, almost anything would do (*). If you turned up on something really odd, you might get folk asking about it but mostly because they were interested in it, very rarely in a judgemental fashion.
It is a little while since I have ridden with this sort of winter training group (my racing days being well behind me now) but when I've encountered similar groups riding recently they have all been riding the same kind of bikes, almost clones of one another; different coloured frames and different groupsets being the main variations. [e.g. few use a fixed gear machine as a winter training tool; it is more likely to be dismissed as something that is fit only for urban hipsters. ] It seems certain to me that (at the least) there is some kind of groupthink at work even on winter training rides and that if you turned up on something else you might not be accepted as part of that group. In summertime it seems even worse; there are droves of cyclists who feel obliged to ride a 'racing bike' when riding with their club even though the closest they might come to actual racing might be a sportive of some description once or twice a year; I think that there is often bike snobbery at work here.
I well remember a friend being told that their bike 'wasn't good enough' to race triathlons/TTs on even though it weighed about 19lbs, had tribars, fairly aerodynamic wheels etc. The main objection of their (triathlon) clubmates appeared to be that (ironic bearing in mind the RTTC champion around that time...) the frame had canti bosses on it; it wasn't built for fat tyres or anything. Anyway they spent thousands (which they could ill-afford at the time) on a supposedly 'better bike' and before it arrived I predicted that it would make sod-all difference. It did, of course, make sod-all difference....
. I'm sure this sort of thing goes on all the time.
(*) as if it needed to be stated on these training rides it became painfully evident how little difference the bike really makes; if you believed that you would soon be persuaded otherwise. Many times someone riding some heap of junk (something that a full blown bike snob wouldn't even think fit for nipping down the shops on) would ride the wheels off everyone else.....
If you never see any variety (eg on training rides) then this presumably reinforces groupthink and equipment prejudices. I think bike snobbery is rife in many clubs these days.