One of the big reasons an E-bike may feel unsettling at highers speeds, say 28 mph for instance, is because the rider of an E-bike may not have enough time on task at those speeds. A trained road cyclist will put in many hours at that speed on flat ground in training rides and racing with others. On descents, they will travel much faster than that. What I'm getting at is, riding a bicycle at speed is a learned skill that requires a gentle touch and movements. The benefit a cyclist without an electric motor has is they have put in a signifcant amount of time to MAKE the bike go those speeds, on an E-bike the abilty is obtained the day you leave the shop. Once these skills are mastered with the appropriate time on task, the squirrelyness will fade away. Bicycles have been going faster than 28mph for a long time.