I have noted where the original article or the comments addressed some additional factors.
In military activities, there is a major emphasis on a principle of warfare called "Unity of Command". That was the reason that a Supreme Commander (Eisenhower as it turned out) was needed for the planning and execution of the liberation of the European mainland from Hitler's forces. However, Eisenhower had deputies from all the services and most of the nations involved in the effort. Bernard Montgomery was commander of all ground forces for the first couple of months after the invasion. Scaled down to a smaller endeavor, such as an individual military service of a nation, it means that the commanders responsible for achieving a national effort should have the means UNDER THEIR COMMAND to be successful. It is a gross violation of this principle to have a RAF-commanded unit operating aboard a RN commanded ship or fleet. It is proper if the RAF unit aboard a ship be commanded by the ship commander.
Modern warfare on land-sea-air (and maybe space) means that the principle needs to have some expansion. The US military now emphasizes Joint Operations, where units of sister services may be commanded by a particular service commander. In an action considered heresy by old-time Army and Marine types, the Army sent the 2nd Brigade of the 2nd Infantry division to Iraq and subordinated it to the First Marine Division. The Marine Commanding General then subordinated a Marine Battalion to the command of the Army Brigade commander. Blasphemy! At this time there are several Army units in both Iraq and Afghanistan that have attached Navy and Air Force people working directly on the ground with the Army people. And the US Special Operations Command has major elements of all the services and also some very specialized people of their own. But in every case, the Unit Commander is actual commander of all subordinate units assigned or attached to the command unit.
So a cursory look at the situation would appear to indicate that the separate services are not required. A deeper look shows that the missions being performed by the services are definitely separated. WITHIN those services are functions that can be performed by properly trained people of any service but the overall knowledge needed for the service function is rather specialized and the training required of a commander for all services would require training until they were too old to be effective. The factors of service pride and esprit must also be considered. An additional factor is that a pilot is not just a pilot. I once asked a highly decorated USAF pilot (more than 280 missions during Vietnam including 80 over North Vietnam) if he would like to try to land his F-4 on a Navy carrier. He gave me a succinct "Not only NO but HELL NO!"
Another factor I have not seen considered is that the war the nation gets is seldom the war the nation has prepared for. The WW1 Allies were not prepared for the realities of machine guns or of tanks. In WW2, the British and French were not prepared for the Blitzkrieg while the US was not really prepared for ANY kind of war. The US was not prepared for Korea or for Vietnam. In Afghanistan and Iraq, the US was not prepared for the unconventional war that we got after the initial battles. In all these wars, the wrong generals were weeded out and the right ones brought in - after a time. And the strategy and tactics, tools and weapons, changed each time to fit the needs of that war. So there is a major danger in postulating that the next war will be like the last war. Two things are certain: there will be another war and it will not be the same as the last one. War planners always face the problem that they cannot win, they cannot tie, and they cannot quit.
So the only thing the the planners really have to go on are the Threat Analysis and a cloudy crystal ball as to the war they will face. The worst problem is the politics of a democratic nation. One politician says to an ally "We will be with you till Hell freezes over." Another politician says to an ally "If the fires of Hell are banked even a little, we are out of there!" And enemies change - I am old enough to be told about the vile Italians, the brutal Germans, and the evil Japanese. Now those countries are actually some of our best Allies (after the British, of course!). Which all means that military planners must devise a force and equipment structure that can sort of meet any threat and must meet the economic constraints placed on the solution chosen. A difficult task.
Lastly, no single service can fulfill all the requirements for the winning of a war. E.g., air power is a NECESSARY BUT NOT SUFFICIENT tool to conquer an enemy. The same holds true for sea power. In WW2, the air forces repeatedly said they could defeat the will of the enemy with bombing. They could not. Land troops can potentially do everything that conquering an enemy requires but without air and sea power, the land forces will take much heavier casualties and may not be able to conquer. To sort out the appropriate budgets for each service requires the most unbiased yet knowledgeable of people - and those kinds of people are in extremely short supply anywhere.