Back in the day of drop-ins, you had Ultrafire (C8, ’501, ’502, etc.), Solarforce (L2 series), NexTorch, the OG Suefires, and a plethora of mfrs who made lights that took drop-ins. Hell, even the Gen-I C8 had a pill instead of integrated shelf (Gen-II and up).
My cheap C8 clones used crappy thin Al pills but also accepted thicker heavier brass pills for real C8s. As long as not too high-strung, I could still use the crappy pills.
All my LEDs, drivers, etc., weren’t for upgrading lights, but for building custom drop-ins. Hell, half of what I bought from FT early on was empty D26 drop-ins. SMO/OP reflectors, XP/XM center holes, typische NANJG drivers, etc.
So I could change from a throwier SMO/NW/XP-E drop-in to a floodier OP/WW/XM-L drop-in to red/green/UV, whatever I had on hand. And they all worked interchangeably.
Those could be changed by hand, vs, say, an S2+ where you’d need some tools to swap pills. Doable, but not “in the field”.
Later, the craze for “integrated” lights with custom drivers, sideswitches, enough to wring out 1200lm or more, kinda pushed drop-ins to the wayside. You wanna swap anything, it’s major surgery, and that’s if the damned things weren’t glued shut. So unless you wanted to go that route, you had to settle for whatever crappy lumen-wringing CW emitter you initially got stuck with.
So unless you beat a host to Hell, it was worth it to just keep a bunch of drop-ins and swap as needed.
Tubelights like the S2+, too much of a pain to swap, even if building new pills is fairly easy, so you’d keep individual lights.
Newer lights that are like 100% custom with zero interchangeability except maybe for battery tubes (regular/shorty), you keep ’em as you buy ’em. Doesn’t pay to mod ’em unless you’re really determined.
Would be nice to see pill-based lights make a resurgence, but I’m not holding my breath.