It's still included because it's an iconic gag at this point. It's still a bad translation, but they know fans love it, and that's okay.
It would have been merely old-timey in Japanese, but in English it's rendered as centuries-old vernacular. "Spoony" ceased to be common language in the 19th century. "Bard" in the 18th, except in limited senses referencing archaic usage. No one is that old!
It's not wrong, just a little too far.
And as fenomas pointed out, it was exclaimed in a fit of violent rage. That is not the kind of thing one would bark out in a situation like that.
The reason why it's in every single FF4 translation is because it's such a ludicrously bad translation that it came out the other side and ended up funny. It wasn't intended to be a comedic scene, but it's become one in the minds of English-speaking fans.
(Also, Woolsey never translated FF4... he just did FF6, plus a TL of FF5 that never saw the light of day because Square pulled the plug on the US release on account of the game being "too complicated" for Americans. And while Woolsey is a master of dialogue who contributed a lot of iconic lines, his Japanese comprehension was actually pretty poor, and his FF6 introduced a number of plot holes that weren't in the JP version. The GBA translation is objectively better, and if you want both a good TL _and_ Woolsey's dialogue, there's a romhack out there called the Ted Woolsey Uncensored Edition that combines the most iconic lines from Woolsey's script with a translation based on Legends of Localization's thorough analysis of the script.)
Also, I honestly thought Woolsey wrote that line because it was so his style. Apparently this is a common misconception.
https://finalfantasy.fandom.com/wiki/You_spoony_bard!
> Tellah
> original: きさま あの時の吟遊詩人! きさまのせいでアンナは!
> literal: You! You're that damn bard! Because of you, Anna's...! (The word used for both instances of "you" is "kisama", the single rudest way to say "you" in Japanese. Because of its harshness, "kisama" is somewhat akin to "you bastard" or "you son of a bitch" in English.)
> SNES: You're the bard! You did this to her!
> Edward
> !?
> Tellah
> original: きさま よくも娘を・・・・
> literal: How dare you do this to my daughter... (Again, "kisama" is used for "you".)
> SNES: You swindler!
> Edward
> original: ちがうんです!
> literal: It's not like that!
> SNES: Please! Listen!
> Tellah
> original: なにがちがうと いうのだ!
> literal: How the hell could it not be like that!?
> SNES: You spoony bard!
I'm all for localizations that take liberties with the translation (see: the best parts of Woolsey's dialogue in FF6), but looking at this in context, it makes no sense. Woolsey's famous lines, like "Welcome to my barbecue!", belonged in context and didn't look out of place. This is just a non sequitor.
If you asked me to give a localized angry response to "Please! Listen!", I'd probably go with something like "I'm not listening to YOU!". Or if I wanted to be silly with it, "Why would I do that, bard-brain?" (OK, I'm not the best dialogue writer...).
[0]https://www.merriam-webster.com/dictionary/spoony