I’ve had to back off of 10 lessons a day because I can’t actually remember more than 4 (and a 5th with difficulty) new kanji or vocab a day. I do reviews several times a day to keep the sessions as small as possible. Even then, I get plenty of items wrong, and don’t progress at a perfect rate for my number of lessons. I consider 15-30 days for a level a success. This is a sustainable pace for me. It might be too slow, or too fast for others.
It isn’t about laziness or not devoting the time. It is about not getting overwhelmed with reviews you can’t answer correctly. I don’t see a problem with telling new users to slow down if they run into trouble.