That Grammarist post is completely misleading, not to mention contradictory.
A) IF "More so strictly means that to a greater degree ...," then the word "more" IS a crucial element of the sentence:
Gina is studious, and Eleanor is more so.
B) The sentence is stating that "Gina is studious," and that "Eleanor is more so." Meaning, while Gina is studios, Eleanor is MORE studious than Gina. Therefore the word MORE, IS crucial.
C) You cannot simply replace the word "more" with "less" or "equally" because those two words are in no way equivalent to "more." If you stated that ...
Gina is studious, and Eleanor is less so.
... you would be stating that Eleanor is LESS studious than Gina, and therefore it is not an equivalent sentence.
The logic behind the Grammarist site post on this topic is baffling, to say the least.
Anyways, in my opinion, while "moreso" is used MORE (not LESS or EQUAL TO) in the US than in other places, it would probably be wise to use the two-word version (more so) than the one-word, just because it is more widely acknowledged. Acceptance is a bit irrelevant considering the differences among many languages around the world.