.....Personally speaking, heavy cues are relics and are more akin to memorabilia from days long ago than functional use as one of my playing cues.
Easier ball movement means I have to take juice off my stroke. I prefer putting juice than taking some off. It's crucial depending on what kind of player you are.
Efren is an anomaly and isn't the norm. To be honest, he probably can shoot with any and doesn't have a preference. It probably just happens the cue he is shooting with right now is 21 oz.
I recommended a lot of cues on here but I get the same response, "Those specs are horrible."
Also, it is up to cuemakers to make specs that are playable in today's market and climate.
I think 19.5 is as far as I go, shot with one to other night and it was pretty good. I like to float around the 18 mark as I find it easier to give more juice than hold back the juice.
I like to compare cues to race cars and if a cue maker can add all the fancy stuff while keeping weight down is a beautiful thing.