I'd say being "powerful" is more important than being both flexible and/or strong. Especially in the higher levels. Sometimes powerful and strong go hand and in hand, but not always. Depends on how you define strong. I'd say having that natural spring in your legs and shoulders - like that ability to generate a lot flight/air compared to others is what matters most for gymnastics potential.
There is also slow vs fast twitch, which is to be considered as well. Flexible slow twitch hitting a progression ceiling the earliest.