Sprint and pause is a valid strategy, but not everybody profits from this style and a lot of people actually do very badly doing so.
A lot of kids in school learn like that, binge learning shortly before their exam, doing the bare minimum during class and forgetting evrything during holidays… still some will become able to speak and use the language just fine after a few years in school. The majority won’t touch the language after school though, unless they need it for something.
Without the external force of school a sprint and pause style often fails in the pause phase, as folks just aren’t restarting after the pause or have pauses of months/years
they can also easily fail in the sprint phase if they try to sprint for way too long. 3 weeks of sprint are usually way better than 3 months.
I read language schools with shorter durations, but taken regularily are more effective than one long language school for example. Cause when motivation is high, you can power through more in shorter time, but when motivation fades after a while, it doesn’t make sense to force this high speed, cause motivation is also key for retention. In addition it seems to lead to burnout for a lot of people, explaining the long pauses after an excessive sprint.
Pauses where you do nothing are also not the most effective ones, though it’s still possible if you don’t care to much about effectiveness. Engaging with the language in some way that’s easy, casual and fun for the level you reached while doing reviews without adding new things gives the brain time to relax a bit and settle what you’ve learned.
Personally, I’m the sprint and pause type of learner myself. I think a lot of people are. My brains gets bored when I try to stick to a routine and then I can’t learn anything at all anymore. Schools seem to be all about drilling the importance of consistency into young heads, even when a sizeable portion of the students won’t deal well with that.
Having said all that, trying to rush all the way through to N3 in such a short time when you already feel a burnout on the horizon is not how you do sprint and pause learning at all. There is a severe lack of pause to let the brain decompress, motivation and egagement goes down. You probably already noticed a retention drop and maybe even a feeling of dread when you think about your review pile.
The question only you can answer is, do you thrive on habits or do you despise them? If you do well with habits (like keeping on top of your reviews for years) then just slow down, you’re in the marathon group, pace yourself and let the habit take over. If you have trouble maintaining habits, then pause until your brain is fresh again (takes longer after burnout, so avoid that at all cost!), and then go for another sprint, just make sure you’re not trying to run with the marathon group. Lots of sprints can get you the same distance in the same time.