I hate to hear comments like "I'm doomed to have bike fit problems forever". In the words of T.E. Lawrence, "nothing is unwritten".
We can generally assume a bike is symmetric, and that the rider is asymmetric. A Fitter has to analyze, assess and test those discrepancies, then aline and accommodate for them.
If, in your case, you've gone thru a fitting and are happy with the result, we still have to solve this point-of-contact issue. What is causing the 'hot spot' on one side, where is the imbalance? Let's eliminate the possibility that your saddle is bent (can happen, after a heavy crash). Let's see if we can pull this apart and learn where the issue begins.
Try this: take your pedals off the bike. Put the bike in a trainer and sit...no shoes, just let your legs hang down. What is the sensation on the saddle - is the weight distribution even on your sit bones? If you tell me that no, I still have a hot spot on one side, then we might be talking more of a medical issue than of a bike fit. However, if you find that you and the saddle get together down there 'ok' now, that the weight distribution is better, now it's a bike fit thing. It may be that even some of your 'old' saddles, the ones you bought to solve the problem that didn't, may feel ok too.
I'm also assuming you're on a tri bike - is one arm rest more worn in than the other?
In my experience, problems at the saddle start at the feet. Functional discrepancy in overall 'leg length' means that your feet are not level at the pedal. As your feet are never side-by-side down at the 6o'clock position, it may not be easy to understand that your ability to plant the foot affects the saddle. Imagine standing on the ground, but with one foot on a thick rug. You can still manage to walk the length of the rug with one foot planting 'higher' than the other, your bio mechanics can adapt to this uneven ground. However, imagine a two-inch wide railing up yer crotch while you're walking the length of that rug...the sitbones are not level as the pelvis has had to shift to adapt the the uneven ground. Now your sitbones are either moving side to side, or one is slamming up and down. This could be millimeters, but after 20,000 pedals strokes you know how that feels.
In my experience the average amount of shim needed is 6mm, but I have had riders needing up to 10mm of shim under one cleat.
There is more to this, but that's another 200 words. One thing at a time - tell me how the no-pedal-leg-hanging thing turns out. Feel free to PM me if you like.
FIST/SICI/FIST DOWN DEEP