i dont know, he may have been a totally different fighter Manny built his style early on Roach added to it
I honestly think it would have been a bad thing. He would have moved up in weight sooner and therefore would not have captured so many titles and beaten so many great fighters. Also i think that by now with such intense training his whole career his body would have burnt out by now. He came to roach at the right time i believe
true, ariza's training method would not sustain a long career since his drills are quite a torture for boxers. but of course, ariza might do it in a different level defending on circumstance. but it's clear as day that it would not be actually bad if roach started on the offset of pac's career and had him a world class coach trainer in such an early age of 16. pac could have avoided overstaying at 112 when his body is fast growing and suffered a KO. roach would ahve immediately advised him to go up to a more comfortable division for him and be a two-fisted fighter in a much earlier stage of his career.
as it is he is an ATG, idk if changing things would make him better. if he started with roach, he would be fighting in the US right, well there is stiffer competition in the US than in the Philippines and he didnt have an amateur career
well if he started in the US, he won't be fighting stiffer opposition since he would be fighting boxers his age. he started pro in the philippines at age 16 fighting fully grown man even if some of them are what you called bums. naturally, pac would be matched with the same record in america.