It's harder to take/hold an e-bike above the motor's top speed, and even the most basic kit can triple the weight of the bike. E-bikes are relatively sedate. Given the importance of tougher tyres, and less so weight and aerodynamics, the idea of a legal electric road bike baffles me. It just doesn't make any sense.

The only benefit i can see is to mid-drive it and cheat the speed restriction, so it gives you a little help at high speed, as well as hills.