Efren Reyes is probably the greatest all-around player who ever lived. I feel honoured to have seen him in his prime, and yes of course, he's no longer his former self. I still love watching him whenever and wherever I can.
To answer your question specifically, I never saw him play 10-Ball in his prime. We can only speculate what his break would have been like if 10-Ball had been the game of choice back in the nineties - of course it wasn't, but since Efren's no doubt the greatest Rotation player ever, we should not underestimate how well exactly he could do in all related disciplines.
"Overcome SVB's break" implies something that as an instructor I have to remind my students of all the time: one doesn't need a monster break, that is, one doesn't need to be able to make several balls and get a cosmo in order to do well. Make one ball and get shape on the 1 is well within the reach of most good breakers, and it would be silly to suggest Efren was any less than a very good breaker in his prime. And I'd estimate his chances of getting out from there as greater than anyone else's "cosmos".
(On an unrelated note, if I had one wish free, it wouldn't be for a monster break of my own - one object ball each time plus shape on the lowest-numbered ball would serve me just fine!)
Admittedly, the break may be the relatively speaking weakest weapon in Efren's arsenal, but think about it: how could he have been so dominant in 9-Ball for decades if indeed his break were as "bad" as some say? It's just that he does everything so well that he makes his break look like his Achilles' heel.
Greetings from Switzerland, David.
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„J'ai gâché vingt ans de mes plus belles années au billard. Si c'était à refaire, je recommencerais.“ – Roger Conti
Efren never had a weak break per say, but he always used a break in the 18-20mph range or a cut break. While that is acceptable and can even be used at the highest levels in 9 ball because it is easy to make a ball on the break even with a soft break, I don't think that will cut it in 10 ball where dry breaks are a real issue and your opponent is breaking and running every other rack. You mention rotation, but in rotation there is very little advantage for the breaker because it is so difficult to get out.