Starter Weapons That Still hold Up Till The End Of The Game

The pistol you start with in STALKER 2. That thing costs nothing to repair, somehow does more damage than .45 ACP, despite shooting peas, and can be suppressed. Ridiculous.

Also the plasma cutter from Dead Space. Stays dependable the whole game.
 
You can get through a lot of games with starter pistols if you have a good aim. GTA IV on mouse and keyboard, pistol, headshots, all you'll ever need. I recall the HL2 pistol as being pretty useful as well. The newer Deus Ex games, perfectly viable with an upgraded silenced pistol for a lethal stealth run.
 
Doom has 2. The fist is super strong once you find a berserker pack, making it very useful when you don't wanna waste ammo on pinkies, for example. The pistol remains a useful sniping tool - as long as you press the button for every shot it has absolute precision landing in the middle of the screen every time, very handy with distant chaingunners, who are a nightmare to deal with otherwise.
 
Pretty much anything in Dark Souls.

One of the reasons I love the series. Almost everything is viable and therefore relevant, even among Demonic/ God like weapons.
 
The first weapon in Unreal. Unlimited ammo, you can charge it, it has like 4 upgrades hidden in the game. With an amplifier (it was I think?) and the charged shoot you could kill the last boss with like 3 shoots, if upgraded completly.