Spending time with just DS1 didn't stop him being a naughty boy all the time, just while he was getting the quality time.
I actually agree 100% with berrme's post. My DS1 is nearly 3 and he's had a whole year to get used to having DS2 around. But he still is the most happy and content when he is one on one with me (or DH). But that's just not reality for him, so he has to learn to live in this family and share his parents with his brother.

DS2 gets very little one on one time, bless him. I think when DS1 is not around he wonders where all the noise has gone, and why no-one is bashing him and stealing toys!

I do try to give them both a bit of time with my full attention (i.e. distract one with trains or food and then read a story to the other), but you do the best you can, and sometimes it doesn't work out that way.