Those sentences which you quote from that book are rather strangely worded. I can see why they easily lead to incorrect interpretations.
An equity index (e.g. QQQ) is the composite of multiple underlying companies' stock tickers. This equity index will thus move according to the collected moves of all these companies together. As such the index gives an impression of the total represented market. As each company only has a limited influence on the index, are movements of the individual companies less/hardly visible in the movement of the index.
This sentence "because no one trades the index" sounds rather strange. In principle he is correct: an index is the combination of multiple underlying symbols. As such, you cannot trade the index: it is an artificial number. But there is a huge amount of trading in ETFs and futures which track this index (plus options derived from these). In your example: QQQ and NQ/MNQ.
I think that the author is rather harsh in the last sentence ("For many technicians, the index is useless for the purpose of evaluating individual stocks, which is what most investors would be expected to use SR to accomplish."). Many people use the index to get an impression of the overall market direction. This could provide extra color in case you want to decide how to trade an individual company's stock. Having said that, when a index has reached a S/R level it does not mean that the individual company has reached a S/R level.
If using S/R on the QQQ works fine for you, then you should continue using it.
I appreciate your reply. I had wondered about this exact question I quoted before....so when I saw it answered this way in print, I was taken aback. Because I have not been DAY trading this way very long, I wanted to pass it by seasoned traders. Price, at least the S/R lines I draw now, do seem to stop on the lines I draw. Even if they blow through or momentarliy stall at the first resistance line, say on the way up, they seem most often stop and pullback at the next. That helps a lot.