You’re missing the point. It isn’t about the individual training of the soldier or marine; it is the function of the unit, and what their TOE and their distribution of MOS. Army Rangers are an advance fighting force; their job is to drop in behind enemy lines, disrupt logistical lines, and provide advance recon for a succeeding major infantry or combined arms assault.
The Marines are similar in that their job is to drop, swim, or roll into the maw of the enemy to secure entry points and provide deep reconnaissance, but they do so with less logistics and planning, potentially for an extended period of time. Although the Marines necessarily specialize in amphibious entry, there hasn’t been much call for this in recent conflicts, and so their mission overlaps some with Rangers and other Special Forces. However, the Marine Expeditionary Unit (MEU) is an almost completely self-conatined unit both in terms of logistics and fire support, and so can get on station and maneuver much more quickly than the more logistically complex integrated units like the 75th Ranger Infantry Regiment, which is dependent upon Air Force support for transportation and air support.
Units like 1SOFD-D and Navy DEVGRU (colloquially but inaccurately known as “Delta Force” or “SEAL Team Six” respectively) are known as Special Mission Units that obtain special training, weapons, and equipment and are specifically tasked to counterterrorism, deep penetration extended reconnaissance and sabotage, and a variety of deniable and covert operations. While these are drawn from the ranks of Rangers, UDUs, Marine Force & Division Recon, et cetera, they have peculiar training and support. You may be excused for thinking them all to be interchangeable between units and with standard Airborne and other elite conventional forces as the same mentality exists at the command level, often leading to these units being inappropriately deployed for the wrong kind of conflict. (See Pete Blaber’s The Mission, The Men, And Me for a devastating account for how this philosophy resulted in hideous miscalculations during Operation Anaconda.)
And if you drop a Ranger or SEAL into a Marine unit, he’s going to get chewed up and spit out, regardless of his battlefield skills, which highlights a point, to wit that military units are not trained, equipped, and deployed as a mob of individuals; each unit is a fighting element which moves, fights, and dies all of a piece. The Marines have a particular function, and while many techniques and functions of the Marines are duplicated in other services, no service integrates a self-contained fighting element like a MEU that can be deployed with the same degree of speed and decisiveness.
Stranger