"Bill
Some answer for the OP:
Yes, you need to buy KERS to be competitive, even in non-2d. Your drivers will use it on their own at absurd times and most times not use it all - but they will use it.
To compete at top levels though, you need to buy the 2d where you can use KERS for an entire lap (even in braking zones!) to get ridiculous lap times and close impossible gaps. It's a Pay to Win feature.
With that said, the game is too buggy to be worth what they charge for the 2d. The only reason I keep playing is the friends in my league, and the calming thought that I've only wasted my time playing a game when it crashes with 3 laps to go, not any real money.
2D viewer works fine for me, I've had no issues in an everday 100% league race for the past 2 months.