Doesn’t that seem a bit odd? To go from N5 to N1 in only a year when people go to college for 4 years and barely are fluent if at all?
Perhaps contrary to popular opinion, universities teach things at a relatively slow pace–at least in my opinion. Now more than ever, curricula are oriented to a certain lowest common denominator. That’s inclusive not only of ability, but also motivation. For a highly motivated learner, you can easily outpace most university programs.
But also keep in mind that a university student studying language will also be devoting a lot of time to other things, too. They have to satisfy general education requirements, and language programs often include other prerequisites, like humanities.
That being said, your pace matches mine pretty closely. I smashed through all of Bunpro N5 in two days (which I came to realize was a mistake when I saw the huge number of reviews it produced). I then switched to just five new items per day at N4, and then have only been doing three per day since N3. That helps to moderate the number of reviews. I’m early in N1 right now and expect to finish it in 50 days (for 270 days overall to get all items into review). Perhaps the key difference for me is I started Bunpro after I was already 18 months into studying Japanese, so maybe half (or more) of the items that have come up were not new to me.
Just keep in mind that studying grammar alone doesn’t mean you understand the language, let alone would be able to pass the N1 exam. You also need vocabulary. A lot of it. Tens of thousands of words worth. You also need to spend a lot of time and effort speaking and listening to Japanese. Those things are by far the bulk of the work. The grammar is easy, comparatively speaking.