I had to break a jig off the other day. The rig was 40# mono - blood knot - 40# seaguar - SD jam knot. On my Sealine 50, I had to crank the drag down to max, thumb the spool, and lean into it with EVERYTHING I have to snap that line at the blood knot. Now, a dropper loop is virtually identical to a blood knot, and should affect line strength similarly, at least when tied correctly.
I think part of this problem with fishing the dropper loop, or any type of loop knot, is that everybody is using braid. Doesn't stretch so it's really easy to break the knot since the shock absorbing qualities of the mono aren't present. Working the drag perfectly becomes paramount, and I think that for me and other relative noobs who are losing fish, running slightly less drag than conventional wisdom dictates is key. I have my TLD15 set up for about 14-15# of max drag right now on a reverse dropper tied into 50# mono. That's a shitload of fighting power, and realisitically a lot MORE power than it would be with 15# of drag in a mono to fluoro setup, because there's no stretch. Theoretically, it's impossible to break the knots on my rig by just pulling on the end. They're able to withstand 20+ pounds of force, but if a fish makes a sudden run, there's a great deal of momentary stress on the knot, and it can still break.
The point of all this is that I don't think the knots are to blame. At least in my case, there's a nut loose behind the crank
But in general, I suspect that "it's not the knots, it's how you fish them" is good to keep in mind. Setting up your lever drags with a scale beforehand, and knowing how far you can go with your star drags; not to mention perhaps knowing when to back the drag off just a little bit in anticipation of a big run, is going to land more fish than tying a better knot. They are ALL good knots, vetted by hundreds of great fishermen and with plenty of trophy fish to their credit.