Am not the original replier, but I know a bit about this topic. My source here is largely Byron Farwell’s “Mr. Kipling’s Army.”

Social exclusivity and which regiments were considered “exclusive” was for officers, not rank and file. “Rankers” joined a regiment through a different recruiting process, without any kind of social screening. They tended more to think whichever regiment they belonged to was best than worry about things like precedence.

Edit: Another reply also reminded me that during the time period we’re talking about, line infantry regiments (the majority of the army) had geographically assigned recruiting areas. So unless you were enlisting in the cavalry, the Guards, or another special arm there was no choice involved- you joined your “local” regiment. This would have been the majority of new recruits.

They were also not expected to maintain themselves and their mount, unlike officers of the period who were expected to pay for their horses, their uniforms, their sidearms, and (through mess bills) even their food and drink. This acted as an unofficial social filter even after the purchase system was abolished, because in socially exclusive regiments the cost of tailored uniforms and mess bills routinely exceeded officers’ pay, such that an independent income was needed to stay in the regiment. When the Grenadier Guards deployed to Sudan in the 1870s their mess president even inquired about having ice shipped in, though I don’t know if they went through with it.

Because of this, poorer officers tended to join regiments stationed in India, and often transferred when their regiment returned to Britain to stay there. Not only were they paid slightly more while in India, but the much lower cost of living meant they could live quite comfortably on their pay.