I think what Elo's friends mean is that the constants hard-coded into Nelson's rules reflect some assumption on sample size. With a big sample, you'll violate them all the time and it won't mean anything. But they are a good starting point for tuning the thresholds.
If you have many parallel sensors, then yes, a flag that occurs 5% of the time due to noise will flag on at least one twentieth of your sensors. Elo's point, as I understood it, was that they have a long history--which is not relevant to the applicability of SPC.
The long history is not relevant, but the frequency. Most of Nelson's rules are 1/1000 events. If you don't expect trends to change more often than 1000 measurements, that's too sensitive. I don't know what Elo is measuring every minute, but that probably is too sensitive and most of the hits will be false positives. (Actually, many things will have daily cycles. If Nelson notices them, that's interesting, but after removing such patterns, it will probably be too sensitive.)
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