Soos,
Domed pistons really are awful things, but were a product of engine evolution of the time.
Firstly: a high-domed piston has much larger surface area than a flat-top piston.
This means much more heat can be absorbed by the piston (= higher oil temp = burned oil around rings, wrist pins = poorer lubrication at the top of the bore). The heat loss also reduces the cylinder combustion pressure.
Secondly: Extra metal in the dome = heavier = more reciprocating mass = slower engine acceleration.
Thirdly: To get ever-higher compression ratios the dome must push well into the roof of the combustion chamber. As in your pics, valve pockets are needed.
During overlap on the exhaust stroke is when scavenging is most needed, and is most efficient when you can see through the open exhaust valve and past the open inlet valve. You can't do that with high domed pistons.
Then there is the issue of the valve pockets interfering with good swirl patterns.
4-valve heads were the only way to solve all these problems. The XL-250 is a good example.
By contrast, the h.c. pistons used in the BSA and Triumph triples at Daytona '69, '70 era are real shockers. I have a pic around here somewhere ...
Fourthly: Don't go carving bits off your piston willy-nilly, as it will upset the balance of the motor. Pistons are manufactured to a weight tolerance of less than a gram, and also must all be the same weight.
Fifthly: No number fifthly.
In among all that I think I may have answered your query.
Oh yeah - piston crowns can now be ceramic coated to provide heat insulation (= lower piston temps).
