The questions here on the forums are divided as per their level of difficulty while the questions in OG graduate gradually from low level to medium and finally to most difficlut level.
So, it could be possible that ur doing more question in the forum that are higher difficulty level. Moreover, I would suggest you to stick as much as you can to the official material.
Yes, but for my sense even the last exercises are not as hard as the ones in this forum. When i compare some questions here which have a difficult level above 700, even if i know how to solve them, i need a lot of time to write down the equatations.