Your text is a bit complicated to understand, but just play more and you will eventually get the handling.
What "switched to new racer" means? Race or racer?
I find it a bit different than Horizon. The handling I mean.
About the career races, well, you start at fixed positions always and they are all silly short races really.
You can use the Free Race to customize a race for you, remove AI completely, etc. So you can enjoy all the tracks there.
To make these career races easier try a suggested car instead of your favorite. It can make a big difference against the drivatars.
Maybe using the racing line at the beginning and for some weeks to understand when to brake will help you.