grammar - is or are for name?

I’ve been reading this article:

I know one of the sample was using ‘is’ for a person name.

“Sasha is older than Mark.”

So, is this sentence correct by itself?

“John Cena is stronger.”

Or is it correct only if it an answer to a comparison question?

“Between John Cena and Triple H, who is stronger?”
“John Cena is stronger.”

How about growth question?

“Is John Cena stay the same through out the years or is he getting stronger?”
“John Cena is stronger.”

I know the last answer is either missing “getting” before stronger or “than ever” after stronger. But I think that is grammatical correct enough of an answer, am I right?

“John Cena is stronger” requires context as to what he’s stronger than. In the first scenario, saying “John Cena is strong” or “John is the strongest” as a standalone sentence would be more accurate than saying “he is stronger”. Saying stronger could mean a lot of things as he could be strong, very strong, or weak, but more powerful than someone who is very weak. By itself, it doesn’t make much sense.

In the last scenario, saying that “John Cena is stronger” sounds a bit odd because of the reason you mentioned, but it still makes just enough sense that someone can still understand what you mean.

Thanks. This is not a home work question, but something important enough i want to get it right before embarrassed myself.

So the second context was right, that was good enough.

“Between John Cena and Triple H, who is stronger?”
“John Cena is stronger.”

Yes, the second context is absolutely right in terms of grammar. However, people normally answer with just “John Cena” because saying “John Cena is stronger” in a reply to “who is stronger” is a little redundant.