Man, this is an MVC thread we are talking about. AND a Mayweather is part of this "discussion"! This is the embryonic stage..... Only another 278 pages of MVC steadfastly refusing to consider all rational counters to go. That said, Senior is a good trainer. But let's face it, senior isn't even the best trainer in his own family (que an MVC "Is Roger Mayweather one of the greatest of all time" thread).
Roger would have more of a shout regarding Mayweather jr's development, but SR had a good run with De La Hoya also for 5 years.
No doubt Senior is very good, but like you say, Roger is a better trainer. And if you have a sibling who is better than you, then you aren't likely to be one of the greatest of all time.
That's a blanket statement that you definitely cannot quantify. To say Roger is the better trainer let's me know you haven't worked with either. Why don't you watch Tim Coleman vs Vernon Parish than tell me who the better trainer is. I'm not saying either is. But what gives you or anybody on this site the maturity or wherewithal to make a blanket statement like that with out any skill-set at all ? That's absolutely crazy !