Videogames built around a progression of weapons are their own thing, no more related to the real world than they are to D&D.But a bodyguard with a gun and a bulletproof jacket isn't the same than a member of a S.W.A.T with complete item. I said bow how example, but I could say other weapons as shotguns, submachines or molotov cocktails.
Don't you remember videogames as Resident Evil or Evil Within where the PCs has to hide in the beginning, but later with enough weapons and ammo can be an one-man-army?
And some players like to mix different titles, for example D&D + Cyberpunk to create his own d20 Shadowrun.
If you allow firearms then most of players will not want melee classes as monk, paladin or barbarian.
Shotguns and submachineguns don't need to be any more powerful in context than crossbows or longbows. Molotovs are alchemist's fire. Pistols are light and easily concealable, ideal for rogue-types just like a dagger or hand crossbow. Bulletproof vests are light armour, full SWAT gear is heavy armour, and their bonuses and restrictions are in line with traditional D&D armour of the same categories.
I've run a 5e cyberpunk campaign using this system which showed a lot of promise but sadly failed to meet its goals on Kickstarter. They use the same classes as D&D 5e, introducing a few additional subclasses, and their firearms deal damage comparable to D&D ranged weapons.
The group had a great time, including both the ranger and the monk.