Marco i didnt say they shouldnt strength train, i said it was a fine balance for thai boxers and i believe that!

and they need to be lean and generally they are very lean, at the top level anyway, that doesnt mean they are not strong.
by lean, i mean that there is nothing wasted and nothing extra to slow them down. someone coming into a 5 x 3 A-Class thai boxing fight needs to be streamlined and have the right balance of cardio, power, strength, explosiveness etc depending on what rules they are fighting and what areas of the require.

being a bit bulkier in mma, in the upper body especially can help the ground game most of the time but it does slow you down.

i dont disagree with you at all about strength training, i definitely feel that some sort of strength training is needed WHATEVER sport you are competing in, but as i said above, the same strength training cant be used for every sport, its a balancing act and a juggling act to try and see what type of strength training is beneficial to each sport. its all trial and error with your fighters, you try something and see how it works, see how strong they are and what parts of the training and strength training were worked in the ring/cage. and its a person to person thing, each person is different and all their training including strength, needs to be adapted to their body.