My friend Rifki asked me, what do i mean by 'only' a Rosh Yeshiva? Well, it's fairly straightforward.
In the business world, let's say in a large finance company, there are different levels of hierarchy. There are the entry-level workers who sell stocks and shares or watch the stock market or whatever they do (I really haven't a clue).There are their supervisors, who have more responsibility. There are the partners in the company, the members of the board, the CEO, etc. This analogy may a bit weak because of my ignorance of the details of the structure of a finance company. But you get the idea, I'm sure.
In the yeshiva world, the set up is similar. (Let's leave out the chassidishe world for now because it does operate slightly differently, but not very differently because nowadays the differences between chassidish and litvish are only a little more than how you dent your hat and what time you pray. Ok, I do exaggerate.) Boys go into yeshiva to learn Torah - entry-level workers. They may have madrichim (student leaders) or older chavrusas (learning partners) for guidance, but they are all entry-level. Some of them become rebbeim, who teach and guide the entry-level learners. Then there are the maggidei shiur, who teach bigger and more 'important' lessons. There are the higher-level rebbeim and the less-high-level rebbeim (in a yeshiva, everyone knows which is which but it's not always through official position appointments, it is just 'known'). There is the mashgiach, and there is the Rosh Yeshiva at the top.
Outside the yeshiva, there is a bit of a parallel track in that there are chinuch rabbonim, who teach in schools (let's stick to the charedi world for ease of analogising). As well as the teaching staff, there are mashgichim (guidance counselors), and menahelim (principals), and in high schools there may be a menahel and a rosh yeshiva, one with administrative responsibility and one with responsibility over the Torah aspect. There are also pulpit rabbis, some with large important pulpits in big population centres, and some with small ones in small communities. There are dayanim (rabbinical judges), who sit on a beis din and issue gettim (bills of divorce), and supervise kashrus (depending on the size of the area, there may be other rabbonim who are in charge of that), and give halachic rulings.
So. There are men who are excellent at learning gemara. They are skilled at it, they are dedicated, their knowledge and understanding increases exponentially every day. They become a rebbe of a small shiur (lesson) of boys. Their lesson grows; they become the maggid shiur of a big group of boys, then they teach the most important lesson. Then they might be considered so knowledgeable that they are asked to become the Rosh Yeshiva. But what if they don't really have the skills to teach gemara, only to learn it? Then they might become a rebbe of a small shiur, but their small shiur may never progress to become a bigger shiur. Or they might become a big important maggid shiur with wonderful empathy for their students, but not have the ability to be able to juggle all the details that make up a yeshiva - when to insist on rigorous learning and when to schedule a hike, when to change learning matter, which commentators will be learned and how many differing opinions will be accepted in their yeshiva, what the tone and style of the yeshiva will be that will make it different from the yeshiva next door or down the block. It is entirely possible, I think, that a Rosh Yeshiva might be less of a talmid chacham than his top maggid shiur is. He just has those extra skills and mode of thought that enables him to run a large company (ie, a yeshiva). But the rosh yeshiva might not be able to be a mashgiach, who usually has responsibility for overseeing the mental health of the students, keeping an eye on who is learning well, who is depressed, who is stagnating because they have outgrown their shiur without realising it, etc, and needs an unusually large amount of empathy, sensitivity, and responsibility.
Outside of the yeshiva, there are rabbonim and dayanim who are excellent at kashrus questions. there are rabbonim who excel at niddah questions, or even in the very complicated halachic fields of issur v'heter, or eruvin, or at unraveling tangled business questions of compensation and ownership. But they do not have the sensitivity to deal with a question that involves people. Emotional implications are lost on them and they cannot deal with the topic competently. Not because they lack knowledge or closeness to God, but because they do not have that skillset. Some rabbonim are excellent orators and inspirers, but when people turn to them for halachic guidance (beyond the basics), they are misled, because these rabbonim do not have the halachic knowledge and inspired understanding to rule in the correct way.
All of these individuals are important, they are all serving God, and we need them. We need maggidei shiur, we need good orators, we need experts in kashrut, eruvin, nezikin and issur v'heter, we need rebbeim teaching small lessons and big ones, and we need roshei yeshiva and mashgichim. We need dayanim. The tragedy arises when we turn a rosh yeshiva into a posek, or make an inspirational orator answer complex halachic questions, or seek emotional guidance from the kashrut expert. When this happens, we end up with a lot of broken, betrayed and bemused Jews. As I think we are seeing now.
Some people can - and do - excel in more than one of these categories that I've sketched out. Very few individuals excel at all of them. To be honest, possibly no one ever has (even Moses was not a good orator). Rav Moshe Feinstein was a posek (halachic decisor) par excellence, but I have heard that his shiurim were never well attended. The Lubavitcher rebbe gave halachic rulings rarely, but the emotional guidance and understanding of people that he displayed and exercised was legendary. Rav Soloveitchik did not give much emotional guidance (from what I have heard), but he was a superlative rosh yeshiva and teacher.
But there are some rabbonim who can understand Torah authentically, and divine the mood and understanding of a whole widespread community, and who can unite one with the other without either compromising Torah or breaking the community. Rav Moshe, Rav Soloveitchik and the Lubavitcher Rebbe could all do this, within their different spheres. We call those people, a leader.
Today, we have a lot of people in all the roles I mentioned above. But we have very, very few (if any) leaders.