Dynamic Difficulty has changed post-patch
The dynamic difficulty was changed to assume you're really good until you make a mistake. So if you start a new profile, and only play songs you're perfect on, the game is going to assume you are an expert, and continually have new phrases start at a very high level. The dynamic difficulty heavily relies on the rate of improvement. So when you start a fresh profile, since you already know many songs, even though you level back down, if you still have 3+ songs you know really well and then play them perfectly, it's going to assume you can maintain that type of improvement.
If you make mistakes, then there's no change in how the dynamic difficulty works. It should behave just as it did prepatch.
If you didn't start a new profile, the only difference you should notice is how difficult new songs start. If you continually sightread badly, then sightreading will get easier overtime, but the system needs to learn that.
We aren't prioritizing experienced guitarists over beginners. The change helped make it easier for experienced guitarists to level up more quickly. If you can, give a little more faith in the dynamic difficulty system. Since you restarted a profile, it's going to be a little tougher if you are playing songs you've already leveled and learned before you reset your profile. It's going to take longer for the system to adjust since it no longer has the history of how long it took for you to get to that point - which is key to the system. Once the system notices that it's constantly giving you too hard stuff, it'll slow down a lot after that point.
Badly enough is hard to explain, as the dynamic difficulty system heavily relies on rates of increase and decrease. If you just leave the game on, and level everything down, it won't necessarily 'rejigger' the system, because once you start playing again, it'll see you're leveling everything up really fast, canceling out the huge rate of decrease, since you just gained a huge rate of increase. The 'rejigger' will happen, when you constantly fail without doing well immediately afterwards.