I have no experience with with larger mono and snell knots, but I use snells all the time with 8lb flurocarbon while bottom rigging. And yes, snells have a weaker breaking strength. I like that when bottom rigging because when my hook gets snagged, I will break at the hook and not lose the whole rig. But I’ve never lost a fish while fighting it to a broken snell knot. As long as you don’t let the fish make a sudden pull with a tight drag, you shouldn’t have issues. However, where I do break fish off is when I am trying to hoist a fish up from the water and they shake. Seems like snells break easiest when that sudden jerk is forced on them with no release of drag. I’ve had lots of breaks that way. And we proved this in the lab one night…well, if you’d call a few guys drinking beer while playing with line, hooks, a scale and heavy weights a “lab”. Without a doubt, snells were the weakest in our informal tests, and would break with even the slightest jerk (with initial pressure at least half of the breaking strength of the line – so around 4lbs in our case) while knots like the improved clinch, palomar and other did not break.
So…I’d dump the snells. Palomar works well for me for forceful and big fish. I use them on all my line to hook connections when trolling for salmon (using 20lb fluoro) and have never had an issue – and those fish hit hard! There are other knots out there…many I’d use before a snell.
However, if the break offs are occuring to one person primarily, it might have more to do with how the knot is tied (make sure to really wet it down before cinching) or how aggressively he fights the fish in (drag too tight). Or bad line?
Just my opinions and observations. Hope to help out somehow.