I wouldn't say that either verse needs to be translated as "whoever," since English is more flexible than that. I would do so just because "he who believes" is strange in modern English, and in other languages like Spanish where that construction still shows up, "whoever" is the go-to English translation. I'm not really sure why you're focused on the fact that
ὁ shows up in the singular, though, since that doesn't always imply a singular individual. My expertise is in Spanish whereas my Greek is at best intermediate, but there you see the singular article used regularly in generic constructions like this. (El que tenga honra, que me siga. He who has honor, follow me. Whoever has honor, follow me.)
I tried to do a search for this sort of construction in Greek, and the only thing I managed to come across was "
ὁ βουλόμενος εἰς τὴν πατρίδα ἀπιέναι," over on the wikipedia page here:
Participle (Ancient Greek) - Wikipedia It literally means "the wanting to go off to the fatherland one," but you see it translated there as
"whoever (= any man or soldier who)
wants to go home…"
These constructions exist, and "whoever" is a very normal way to translate them, specifically because of the Greek grammar.
Oh, I agree. I think we also need to keep in mind the use of exaggeration to illustrate a point, which is common in the New Testament (and in Mediterranean culture more broadly). I am just commenting on the linguistic aspects, here, not the theological ones. If I were to address the theology, my first point would be that we need to consider what
John as the author was intending to convey before we can even approach the question of what Jesus meant. There's a lot of debate on how to even start reading the Gospel of John.