Thinkly,
You noted in
this post that you get frequent rains and also describe that in
this post. With your 9000 gallon pool, and with some cleaning of your DE filter, that can give you water dilution to keep your CYA somewhat in check though it is still probably somewhat high. Note that evaporation and refill does not dilute the water so does not reduce the CYA because the CYA does not evaporate.
More important, however, is to understand that a high CYA with a low FC does not always mean that algae will grow because algae requires more than just a low active chlorine level to be able to grow. It requires adequate nutrients including phosphates and nitrates and these may be low in some pools. Also, some Trichlor pucks/tabs contain copper which will prevent algae growth but with a risk of copper staining. There is also not spontaneous generation so the algae has to get into the pool in the first place, though usually there are algal spores in the air in most places. Also, in your case, most of your reports of FC have been pretty high at 5+ ppm so that also helps even with CYA approaching 100 ppm.
I've used Dichlor to raise the CYA level when starting a swim season and normally use 12.5% chlorinating liquid and did not notice any difference in water clarity except my wife said that after the Dichlor the water tasted a little metallic. There weren't any metals in the Dichlor, but perhaps some contaminant led to the taste experience. With chlorinating liquid, my pool (shown here and here) is crystal clear. However, if one has their water fairly saturated with calcium carbonate, then chlorinating liquid or bleach will raise the pH which could look more cloudy than with Dichlor that does not raise the pH upon addition -- also, if you have your TA too high, then the pH will rise over time more quickly with chlorinating liquid or bleach than with Dichlor since the use of Dichlor is net acidic.
When I first started with my pool 7 years ago, I used Trichlor pucks/tabs in a floating feeder. The CYA started at 30 ppm, but after just 1-1/2 seasons of use (about 11 months not counting winter with little chlorine usage) the CYA was around 150 ppm. We get virtually no summer rains and I have a mostly opaque electric safety cover and used a pool cover pump to remove rain water to the sewer over the winter. I also have an oversized cartridge filter only cleaned once a year so I have very little water dilution. When the CYA rose, the chlorine demand went up and the water started to get dull. Note that I have 400 ppb phosphates in my fill water.
So while not every pool with high CYA will develop problems, the statistical odds are higher. Therefore, the TFP advice is to reduce the odds of getting algae to a minimum at a fairly low cost and reasonable maintenance. It is more about understanding the alternatives and then making informed purchase and operational decisions. If you are lucky enough to not have problems, then great, but that doesn't mean this will apply to everyone. The vast majority of cloudy and algae problems in pools reported on this and other pool forums is due to rising CYA from stabilized chlorine without proportionately raising FC or otherwise compensating. There are also problem reports in SWG pools due to a low FC (usually 1-2 ppm, sometimes 3 ppm) relative to CYA (usually at 80 ppm).
Richard
To each their own.