Something to consider is that one reason why spec racing is more popular is because "slower is faster" meaning that having too much motor can be a bad thing, causing you to blow corners and spend too much time on the brake where a slower spec motor allows more smooth throttle control and less likely to break traction... it's not uncommon for 13.5T spec motors to beat guys running open mod... yeah a mod driver can turn a faster hot lap, but what wins races is consistency and it's a lot easier to get better consistency with a spec motor

A seasoned pro driver on the other hand can handle a hot motor and knows how to tune their radio properly for a given track condition.