I'm glad you framed this as a general observation and not an absolute statement.
That's good.
Let me first say that I do agree that a Floyd Rose style locking nut is preferable to a behind-the-nut string lock. So, in general I would agree that a behind the nut string lock is probably not the best solution...but it does vary from installation to installation.
Back in the '80s, I had a Washburn Wonderbar on my '74 SG. I still have that tremolo. Anyway, I did not personally install it at the time, as I was new to guitars. I had it installed by a guitar shop shortly after I got the guitar. They installed the lock behind the nut as that is what came with the Wonderbar kit. I used that system for many years without any problems and it returned to pitch very nicely. I do not know if the shop made any modifications to the nut slotting to make it work better with the string lock, but I doubt it.
Incidentally, one popular user of the Washburn Wonderbar is Pat Simmons of the Doobie Brothers. I believe he still uses it to this day. It's a pretty decent system, but it does not have quite the downward range of something like a Floyd.
The first guitar i ever bought for myself brand new was a 1983 Ibanez DT555 Destroyer.
It had the Ibanez Pro-Rocker Locking Tremolo, that was the forerunner of the later Edge Tremolo. It had a locking nut behind the nut. I had a lot of tuning issues with that tremolo, most of it with the fulcrums and some with nut slot profiles and the lock nut, which was held with tiny wood screws, woukd loosen up with Tremolo use.
Eventually, about 1985, i had Wayne Charvel convert it to a Floyd Rose and move the lock nut so that it replaced the stock nut and it was fantastic after that. The repair was so good that you had trouble telling it had been fixed.
I'm not a big Tremolo guy, but i like my YelloStrat 6-screw tremolo for projects where a Tremolo is desired. Its good enough and stays in perfect tune.
I can drop it 11 semitones, bar-to-the-wood, which is good i think for most things, anyways.
I got offered the job at Fender after someone saw my "11 Semitone Divebomber" video, so for a stock Fender tremolo, that's pretty good performance.
However, i think the 1-3/4" wide, 1-1/4" thick, deep 'V' profile, roasted maple neck plays a secret part in this guitar's tuning stability.


