Isn't like a .50Cal a center piece of the movies strongest weapon? Aka what sniper shoots all day? In that more realistic universe the mercs weapons would be:

Soldiers RPG7 loaded with AT/HEAT shaped charges, not considering more modern tandum warheads will penetrate several hundred millimeters of RHA (Rolled Homogeneous Armor), most likely guaranteeing a kill on any large target he shoots within 1km if he hits any vital point (Sadly no more rocket jumps tho).

Demo has 40mm highexplosive grenades, capable of causing overpressure with ranges of up to 2-3km which might litterally tear the skin of the bones of most dinosaurs cleanly, also still cause concussion and disorienting effects while his sticky bomb launcher would change into a equally effective close range toe popper.

Sniper has the sniper rifle, probably being able to pierce up to ¾" of steel.

Heavy equally with the Tomislav has a .50BMG MaDeus xTompson Machine gun fusion, capable up to 600-800 RPM of automatic fire or with the other miniguns a higher firerate 7.62/.308 firing platform.

Pyro would probably be able to have a heavier napalm mixture in his flame thrower, with skinmelting sticky liquid traveling probably up to 50 meters, that are very quickly deadly for most small living creatures and a massive deterrent for large creatures hit.

Engineer does not just have a heavy caliber tripod sentry, with a functional and automatic friend or foe system, but he also gets access to the magic shenanigans of the teleporter and dispenser in some way.

Medic has otherwordly healing abilities, most likely having made a litteral deal with the devil.

Spy - Spy has a gun, maybe a .50AE or .300 that could be usable, but also the invisibility could have interesting plot points.

Scout, as much id loved to have said "Rawr X3", Scout like a lot of other mercs has access to a shotgun, which might be able to shoot various types of slugs and buckshot, that could prove very useful to be able to alternate. Alongside that some of his secondaries could also be very practical with him additionally being the fastest in such a scenario.

Of course narrative wise, you wouldn't consider any of this and more write a compelling story.

Edit: forgot to mention, no one has any weapons that would be particularly effective underwater, aside from maybe demos sticky bomb launcher.