I'm definitely a big outlier, I was always pretty bad at foreign languages in school, and I was in a very english-heavy daily environment. I have social anxiety too so I just switch to English whenever I'm worried I'll say something wrong.

I studied Swedish in an international gymnasium and then barely passed Svenska som andra språk III in Komvux during the first 3 years I lived in Sweden and I would say I was at a B1 level after that. I went to English-language university and worked in IT afterwards so I wasn't speaking Swedish on a daily basis, just some jobs where we would have the occasional Swedish meeting or I would send some emails in Swedish. After 10 years though I got a Swedish-language government IT job and my Swedish has improved a ton in just a few months. Nowadays after 11 years I'm definitely a C1 or C2. I might trip up and sound foreign on some complex topics, and I definitely still have an American accent, but I basically speak like a native. But yeah, it is very rare to not be able to speak English with someone on the street, but of course, it is important to learn Swedish to make social environments, paperwork, and work easier.

I would say Swedish is probably the easiest foreign language to learn as an English speaker. The sounds are quite straightforward or can be approximated, the grammar is super simplified and nearly identical to English, and most of the vocabulary are cognates with English. A lot of words can be verbified or adjectified so the vocabulary comes quick. Both Swedish and English are germanic languages with tons of French loan words so the overlap is huge.