This goes offtopic, but reading that advice just really makes me want to write this, as this has been on my mind for a while by now.
That's literally a tutorial to becoming terrible. Most of the people asking questions on here are people that ended up stuck because of precisely practicing like that.
I kinda don't like taking myself as an example, but atm I'm #58k. I'm steadily improving and making progress. The maps I'm playing to practice? Lot's of 4* maps actually. I can do pretty good and fc lots of mid 5* maps and easily play and pass high 6* maps, but are they good practice for me? Up to mid 5* is still decent, but above that? Not really, detrimental in fact.
The reason for that is quite simple, primary skill comes from being able to read maps. From playing all these high star / high ar maps, you'll get lots of practice for moving fast etc, but zero practice in consistency and reading, in fact you learn to read in bad ways that make you more and more inconsistent.
I consider maps good practice, as long as I can kinda keep up with my eyes when trying to read them properly. Sure, they need to be challenging to a degree so that I improve from it, but not to the point, where my eyes can't follow at all, which would reinforce a different kind of reading, which is less precise but easier for you to maintain.
On top of this, whenever I practice, I always have a few things in mind I'm trying to improve on and I can't focus on improving in those areas when a map requires my full attention to just be able to play it. This is where 4* maps start shining. For my current level, they're simple and not very demanding, but not easy. It challenges my accuracy and consistency but still allows me to direct my full attention to areas I wanna do better in, such as having all my attention on how I move my eyes/read, or how I press each circle/slider, or how I aim. I can have very focused practice to beat bad habits on those maps and that is very valuable.
For those that are reading, for the most part, these easy maps will be low 3*s instead. People really move up the star difficulty way too fast and then when given the advice, they all say "those maps are too slow for me, I can't play low ar/slow maps, I always go too fast". Well duh, that's your problem, fix it, stop dodging it.
It always pains me a little when I see people at #100k-500k play maps that I consider too difficult to be good practice and then wonder why things aren't going well.
Ontopic:
You'll just have to accept that you'll do worse for a little while, but with a little bit of practice and time, you'll quickly get used to it and do much better. Mouse only is very limiting.