REALZEUS:

Sportscars were nearly as fast beacuse F1 cars were more restricted. Left to their own devices, F1 cars would be incomparably faster than sportscars. If left unrestricted race cars of all sorts would be too dangerous and ultimately undriveable.

No quite true.

F1 cars have  been designed for sprint type races on shorter circuits. (there was a time that F1 and sportscar raced together).

Sportcar's (Prototypes) are designed for longer circuits with longer straights. (Le Mans)

Prototypes (in general) spend longer periods of time during a lap at full speed.

F1 need to accelerate much quicker.

Obviously the F1 is quicker around a lap (much higher cornering speeds and acceleration), but in a straight line the Sportscar will have the advantage. Especially due to aerodynamics and gearing.

Remember the long tails?

Unrestricted, both would be un-drivable!

The problem is that regulators have a compulsion to constantly regulate. They feel that they need to constantly change the rules; often to accommodate political and lobby pressure rather than for the good of the sport. They will find any little excuse to "mess" with the rules every year (and in many cases even during the year)

They start off with poor rules and then spend the next decade modifying them, until eventually a "new" set of rules get written. Then the cycle starts all over again.