For starters, it's selling the game short. In today's age adult gamers have busy professional lives and child gamers are all hopped up on Ritalin and sugary breakfast cereals, so first impressions are important. And the first impression will be a game full of poorly-balanced guns made from glue and sand, with aim waver like there are hummingbirds worrying at your fingers. Horrible weapons becoming more effective over time is kind of the exact reverse of a difficulty curve.
Agreed. Except it doesn't have to be this way. A multiplayer FPS can have "classes", so you start at each spawn with your newly selected bod, who not only happens to have a sniper rifle, but the skills to use it - and a nice frondy costume to boot:
You can pick up weapons from dead bods, but a sniper shouldn't expect to do all that well with a pair of sub-machine guns. No John Woo. Yet, if he were to stick with them, the more
positive kills he got (that is, enemy kills that are entirely his and not helped by an assist which he then survives for 5 seconds for the "kudos" to register) the more his hidden RPG stats would auto-allocate. Also, if he came to prefer the sub-machine gun over the sniper rifle he would be slightly less acquainted with that weapon were he to go back to it. So, a bod would be best sticking with the weapon from their own class that they had been "trained in" and they would not be instantaneously expert with an unfamiliar weapon or vehicle.
Yes, they would get better with their spawn weapon the longer they used it, but only provided that they used it well. Miss enough times and their skill would nudge back down, eventually slightly below where it was when they came in "green". The original Halo gave your Marines a kind of RPG stat so that the longer you kept them in combat, alive, the better at sniping they got, etc. The game would just have to throw more enemies at you to re-balance this, so in getting more skilled you are asking the game for a more unnerving challenge. Difficulty then needn't be selected at the outset of a game - just give it to them on Normal, drop quietly down to Easy if they die at a particular checkpoint or between completed objectives 10 times in a row, just so they don't quit the game in frustration forever and never buy the sequel; also, ramp the difficulty up to Heroic as they demonstrate their in-game skill, by hardly dying once (leave Legendary for a second playthrough unlock once all levels of the game have been beaten on Heroic - don't do the damned irritating thing of making you reattempt from the beginning of the level/game to adjust the difficulty when you have no idea how hard the developer has pitched it).
For main course, it forces you to invest in weapons that may become obsolete. Resident Evil 4 pulled a very mean dick move - after spending the first chapter blowing sackfuls of zombie farmers' stolen pocket money on upgrades for the shotgun, rifle and pistol, suddenly the merchant remembers he has some better models you can trade in for, which have to be upgraded from scratch. So you either write off the upgrades as a loss or stick stubbornly to the inferior models, and then who's the Luddite?
Surely, this Merchant could redeem the value of these upgrades? It is unfair to criticise a game mechanic based upon a poor implementation.
And for pudding, different weapons are used at different times. Upgrading RPG-style only makes sense if you've got several methods for dealing with the same problem - that's when you choose what sort of character you are. That's role playing. But in a shooter, if you're faced with snipers and have been plugging all your points into shotguns and pistols, then you get to eat shit on toast.
This can be easily solved with some lateral thinking. The problem with a Campaign-based FPS having RPG elements would be as you described, yet I am starting to feel a bit lonely playing these one-man army games and would like to have some NPCs to fight alongside me and maybe order out to flank the enemy, take stupid risks, etc. Now, it occurred to me that games could have you Hot-Swap between each line-of-sight member of your team (as in Battlefield: Modern Combat), which were each specialist classes with their own independently tracked RPG stats and character customisation - one of the best things about Oblivion was the character creator, I don't understand why the FPS genre doesn't support this.
So, playing a Campaign with just 3 NPC allies would be a bit like a mix of Full Spectrum Warrior and Halo 3 Co-op with your mates controlled by AI that knew how to take cover, make sensible pathfinding courses under-fire (not necessarily straight from A to B), suppress targets as you moved and only move when you did the same for them (unless next to a truck about to explode). None of them would be as good as you so in any given situation you would determine which of them you needed to be and Swap into their head to use their skills and equipment at the position they happened to then be in. Some form of target-identification would be required from you to mark a finite set of locations to cover, but this would be as fast as looking at them and giving a heads-up to your team with click of the thumbstick to keep it arcade-y.
By effectively being 4 different classes on one mission, you escape the trap of a single RPG stat-evolved role.