This is competition dancers.You have three different styles of dancing. Standard, Latin and Smooth.
Is it a mistake to try to be up to competition standard in even two styles let alone three. Does there come a time when it is more sensible to drop two of the styles and concentrate on one only.
What comes to mind is that old saying Jack of all trades .Master of none.

Actually 5-- Rhythm and Theater Arts


So how do you account for Irvines and Hiltons winning world Champ. in both Standard and Latin ? ---- plus the numerous 10 dance people

Terence. Which style did each of them give away. Marcus Hilton when he was dancing Latin never did any good in Modern. It was only after giving Latin away that he started to do any good in Modern. Even then it took several years.
He did compete in ten dance. But that made know difference to his placing as a top dancer.
So how long did it take from the time he won the Amateur Latin in 82 - 83 to winning the Professional Modern. I think you will find it took 7 years after he gave Latin away. He also never won the Amateur Modern at Blackpool either. And yet later became one of the best ever modern Ballroom Champions.
Billy Irvine did better and won the British Professional Modern in 62 64 66. And won the Latin in 66. But what about all the others players. And I very much doubt if it could be done today.
Even today the World Ten Dance Champion in both Modern and Latin Amatuer or Professional would be flat out even making the quarter finals at the British in any style.

Not saying it could never be done-- far more difficult as there are far more contenders.

I think most give up due to time , and not capabilty or possibility .
The demands on their time for dems, coaching etc. , are much greater than in the "old " days .

Pity. In the bigger picture, seems to me the difference between all these ballroom (partner) dances is more a question of degree than of anything else.

I think a good analogy would be this---

There are many Doctors that are also Attorneys , and yet they seldom , if ever , practice both skills, time I would guess, being the consuming factor, not lack of ability .