Well, I don't know. Maybe I'm just a loon and beat the shinola (no, obscenity filter, I don't know the difference) out of it.
I'm using a thumb pick, which are pretty much the thickest plastic picks that can be had, and I do dig in quite hard at times. I've only broken strings on fender style basses with Fender style tailpieces that are standard scale, IIRC. I've never broken a string on a short scale bass, never on a three-point style Gibson (single piece and with saddles), and I've broken more strings with my current band than I did in the 25 years before combined - on bass. We'll see how easy it is for me to break strings on the Thunderbird with it's claw/tune-o-matic setup*. In my on-and-off guitar career (I swear, I always applied for bass and was drafted for guitar), I was always murder on strings, and a backup guitar was necessary. When I was a kid and playing in my room, I usually used my fingers, and broke a string about every year and a half.
Now, my last band was a surf rock band, and there I was generally minimizing attack a lot of the time. I think I broke one string in 4 years of shows with those guys. It was a style of music that just didn't call for the same level of dig-in dynamics that the current band does. After one gig with the current band where I was transposing the whole show up an octave due to losing the E, and the backup bass was out in the car - I have consistently brought the backup in and had it ready, and I've used it several times. I'm thankful, because my bringing and needing it has convinced my guitarists to at least bring one backup between them, saving a few shows. But, I still rarely break a string in practice, I usually break them at shows. Go figure.
*Had the first couple of practices with the T-bird, and it will get its first show this weekend. It's generally been a hit. There's some criticism that it sounds a bit muddy on the 2-3 songs I actually play chords on when compared to both the P-basses and Jazz that I usually play with these guys, but not really a problem for live shows. It rocks pretty hard on everything else.
Oh, and ETA: I've become a flatwound through a lot of gain lover in recent years, they have just the right amount of high end for my ear. I always push the low mids when I have an eq that will allow it. On my SB300, the spot I like is with the frequency on about 2 and the level on 7-8.