Back when rear derailleurs weren’t Fugly, that tended to be where your eyes headed when looking over a bike in person or via a brochure.
The XT logo was there loud and proud for all to see. Manufacturers often upgraded this component to draw in punters I suppose.
Of course, they often quietly downgraded something else to offset the expense of the upgrade.
Everyone and I mean everyone looked at your rear mech first, it didn't matter what you were riding, rear mech first, instant judgements made, opinions formed within milliseconds before anything else
I remember saving for ages and buying an XT M735 short cage mech, £40 was a lot for 14 year old me. Put it on my Diamond Back Topanga.
For about 3 minutes I was the cool kid in the bike shed at school. Then Ryan turned up (year above and worked in the local shop) with an XTR mech and crankset on his Eldridge Grade. Instant relegation back to pleb status. Which is where I've stayed since that moment. Thanks Ryan, you git!
All this resonates. First upgrade when meagre Saturday job savings (£1.55 p/h) eventually allowed was an XT rear mech. It looked a cut above everything else in 1989. The component snob in me won't allow for mixing unless it's all top of the range from different manufacturers. If all Shimano for example then it would have to be the same groupset throughout.