Which original incarnation? RE1 Chris was a former Airforce pilot and Jill was a reformed cat-burglar. Both of which were capable, but in no way prepared for what was in the mansion. Capcom re-writing their past every game to make them green beret/special forces was retarded and a good reason why they needed somebody standing over the writers desks with a wooden spoon ready to smack their hands when they started writing dumb shit like that.
Wasn't that the backstory in the SD Perry novel? I thought Jill was always ex-Delta Force, of all things, in spite of being a woman and in her early 20s. I was just referring to the characterization in the OG game. From what I understand it was her dad Dick Valentine (lol) who was a thief and taught her to pick locks. The novel had her be an accomplice to him. Honestly, not a bad idea. Still, Chris and Jill were accomplished military guys I suspect purely because the Japanese turbonerds had no idea what would be an "Average" firearms handler knowledge, and they had to use a lot of guns expertly throughout the game. The novels don't seem to be canon. There's a Tyrant that's just a T-rex. Almost 20 years of foresight regarding Simmons...
S.T.A.R.S in general makes no god damn sense as an American special unit, because the average American cop is already a firearms expert, and trained to deal with threats involving firearms. Again, an era before the widespread of the internet, plus how firearms were in Japan, meant they wanted to cover their bases on "Yeah, this guy and girl can just grab any sort of weapon and operate it without a hitch, and with remarkable accuracy" because, well, the average Japanese dude wouldn't know the first thing about a firearm. They'd probably struggle to take the safety off. Meanwhile Chris and Jill are canonically good enough that they both got through the whole Mansion Incident without getting touched once. That probably involved a lot of shooting. A Japanese cop drawing their gun would reliably make the news. Meanwhile, in America...
But I figure nobody knew this back then.
If S.T.A.R.S were Japanese, they would be completely reasonable. It's a special firearms squad that has received training and equipment to deal with other firearms threats. Basically a Japenese swat/counterterrorism team. The police inspiration carried on in the series: Hunk was given remarkably riot-like armor, a gasmask, and submachineguns. They straight up gave him an MP5 in Re2make, one of the main weapons of Japanese firearm squads.
Anyway, they eventually caught on, because Leon is just a rookie cop and can operate whatever he finds with no issue, and Claire is a civilian who was taken to the shooting range once or twice by Chris and she's comfortable enough to run around with grenades tucked in her unitard pockets.
As an aside, Jill Valentine was Delta Force before Martin Walker from Spec Ops: The Line. And Richard Pearsley, the guy who wrote The Line ended up writing Resident Evil 7. Funny little connection there.
And honestly, I'm just happy we didn't get the alternate timeline where S.T.A.R.S were all cyborgs.
EDIT: Yeah, Re5 Mercs is fun, but just doesn't live up to 4's Mercs. The different loadouts were fun and the different melee and playable characters was fun enough that I've done Barry main caimpaign playthroughs and thoroughly enjoyed them. But they're all the same dude with different guns and melee in the end. Even the odd one out, Wesker, just gets a sprint and a special finicky as hell melee. Meanwhile in RE4, Leon and Ada are "normal", you get a Rambo dude with sick melee, a deadly bow and an instakill swordarm, a dude who goes around snapping three necks per second and basically flash-stepping through the battlefield, and a guy who can gently tap someone on the chest and send them flying across the room.
They really keep phoning it in with the whole different playable characters in recent times. Everyone just has Leon's/Claire's animations, but different pain grunts and huffing sounds, and a different loadout. That's basically a model swap. You could slap Leon's model over Kendo in his special minigame and absolutely nothing would change. Meanwhile, over on PS2, Krauser had unique animations for almost everything, and every Outbreak character had their own walk and run cycle. Even the Outbreak NPCs had unique stats.