I met a few ones who started out in Thailand and barely trained at home or never did. All of them were terrible. Met an australian who moved to Thailand when he was 17 and he had no training back home. When I met him he had about 3 years of training in Thailand, he spent a couple of months every year in Australia but never trained there because he claimed they did "watered down pillowfighting muay thai".
His father married a thai and owned a resort so this kid didnt work or anything, only trained muay thai fulltime so you would expect him to be a great fighter but still after nearly 3 years he were terrible, had no idea how to block a punch or anything. He did look decent on the pads and were fit but were a terrible fighter. Only time he won his fights was again retired thai bums, every foreigner he faced in Thailand knocked him out.
And thats just one example.