I was doing my reviews this morning and got stumped by this:
I was using けっこう as I’d completely forgotten about すぎる:
その冗談はけっこう面白くなかった。
I kept getting it wrong and I thought it was my negative or past tense conjugation that was wrong or that I forgot to do. My question: is その冗談はけっこう面白くなかった correct anyway? If so, is it just the degree of quite, very, etc? Note that けっこう = a lot, hence my confusion. When should I use one over the other?
I can’t say this with authority, but from what I understand the sentence with 結構 would be incorrect. I find that in instances where I’m struggling with the nuance of words like these, it helps to go to a JP only dictionary to pull out specifically what you’re looking for (even if you can’t read it yourself, a deepL translate typically gets the job done)
So here, you’ve got the entries for 結構 and 過ぎる and with a lil doing you can see that none of the definitions for 結構 really fit what we’re looking for here and 過ぎる has (what it seems like to me at least) point 7 which seems appropriate.
After that, you just have to be familiar enough with the grammar point. なさすぎる is an odd expression to english speaking sensibilities but when linked with the literal translation like here it’s pretty easy to come to.
There are, however, a ton of other ways to say ‘not at all’ and it is pretty frustrating in general to distinguish them all 
You can say 結構面白い meaning “quite funny”. So perhaps this is where you are coming from.
For example in an exchange like this:
A: その冗談は面白くなさすぎる。
B: そう？結構面白いと思うよ。
But I don’t think I’ve ever seen it used in the negative.
And in terms of the degree, 結構 (quite a bit) is more reserved than すぎる (way too much). There’s quite a gap between the two.
aha! thank you so much @Gacee and @casual
Yes, I understand that quite is far from very but what you both pointed out, 結構 is never used in the negative, is the most helpful to me.
Could be wrong, but this is how I see them at the moment.
I don’t think けっこう is exclusive to positives. The primary different between the two is that すぎる expresses crossing a line into negative consequences, or being intolerable or unmanagable, which can also be used to be hyperbolic.
けっこう would also imply that it is quite unfunny (or would it be not quite funny?; is 結構じゃない a thing?), but すぎる would express hyperbole better; i.e. intolerably unfunny. ‘at all’ is hyperbolic in this case.
I know, right? Now that I’d been reminded of すぎる and its use, I will just keep in mind the difference between quite and very. When I looked up the lesson for けっこう, all the example sentences were in the affirmative.
So that if ‘nice’ is the negative of ‘nasty’, you can say the japanese equivalent of quite nasty but not say quite not nice.
I looked into this a little bit, and I don’t think けっこう is reserved for only positive sentences (like @kizzlesully said), but I do think it is pretty rare. I had a very hard time finding any examples where this can be seen, but here are a couple:
これはけっこう間違いないなと思いました
これはけっこう焼けなかったほうかなと思っているのと
However, in regards to your struggle here, Bunpro should make it fairly clear which one it wants through the English hints (too much - すぎる, quite - けっこう), but it does help to understand the slight nuanced differences between the two.
Here’s the definition that けっこう takes on in this context:
完全ではないが、それなりに十分であるさま。 (basically, “plenty”)
I want to preface, that I personally do not think that けっこう can be used in this sentence. To me it sounds too much like “quite not funny” in English (note: 面白くない is not “unfunny” but rather “not funny”, which makes a difference). That said, I’ll still explain the nuance here, assuming it does work. When used in this sentence, we get a meaning similar to: “That joke was quite unfunny to me” - it wasn’t completely unfunny, but it was for the most part, unfunny. If I say, “ah, that was quite funny” it means it was sufficiently funny. It wasn’t the best joke I’ve ever heard, but it was plenty funny for me to enjoy it.
Now, if we look at the definition for すぎる in this context we get:
その事柄の程度・限度を越える。
When used in this sentence, we get a meaning similar to: “That joke goes beyond what is unfunny” (essentially: The degree to which I consider to be unfunny has been crossed - it’s not funny at all (and beyond)).
While they are fairly similar in what they’re portraying, there is a nuance to them that does change the meaning. One shows complete disinterest in the joke as it’s gone past a limit of something (すぎる) while the other is used to mention the lack of funniness - it’s not necessarily over a limit, but whatever it’s modifying is “plenty”.
Very interesting. Leaving 間違いない example aside for the moment, since it’s pretty much like 少ない, not exactly clear if a proper negative or not, the second one sounds like the negative can be wrapped under the positive ほう. (Of course a bunpro test sentence would not ask for such acrobatics).
So it could be adapted to something like this:
その冗談は面白いかどうかというと、結構面白くないほうかなと思う。
Any possible mistakes here are mine, and I’d be grateful to hear from more experienced users if this sentence sounds ok or wrong.
Thanks for pointing that out, I don’t know why I never recognized that lol.
I did a little more digging, and asked a native friend of mine - he told me that it’s not “wrong” to use けっこう in a sentence like this, however, あまり would be the more natural way to go. He said specifically: けっこう≫良い意味で使うことが多いね！And just so I was certain, he also clarified that using 結構 in a positive context is more natural (でも、けっこうはポジティブな意味で使った方がよりネイティブな日本語だよ！) hence probably why it’s pretty hard to find example sentences with it being used in a negative context.
Thanks for looking into it! Since I’m just a beginner, I will just keep it simple for my own sake especially since using けっこう in the negative is pretty rare and your native friend said so as well.