Being formerly on the inside I can tell you the answer we were given to the plural of “roshei alfei Yisroel” implying that there is more than one top leader in each generation. I would give it to you straight away but I’ll give you a few seconds to see if you can come up with it yourselves first.
…
…
…
OK. Times up. Here is the official Chabad explanation: The Alter Rebbe [he’s the one who wrote Tanya] was an onov and even though he knew that it was only him [and in future generations only the Chabad rebbe of the that generation] who was the head and mo’ach of all the Yidden, he wrote it in plural to deflect some of the kovod.
I’m sure you all guessed that was the explanation, right?