I don't remember seeing this ad before.

Absolutely true and not stated often enough, Martin. The Power Fin agitator was also a big improvement.  If you really want to see turnover, put a Power Fin agitator in the old tub with the large solid panel between the perforations on the side and the perforations on the bottom.  That really sent the water currents up. While turnover is not everything, there has to be better turnover of the load than there was in the Gyrator agitator automatics.  Maytag used to preach for years that it was more important for the agitator to force water through the fabrics that to move the fabrics through the water, but that was to cover up for their poor agitation should anyone figure out how to look in during agitation like I did at a young age. I spotted that lid switch and held it in to watch what was going on. Between the thrashing that fabrics took from those high fins in the narrow tub and the amount of bleach that had to be used to get good cleaning out of those machines, fabrics aged rapidly in Maytags.

When WP came out with the first large capacity machines, they put a big Surgilator with high fins in them. John had a customer with one and when her son or grandson came home to wash clothes, the large load of jeans broke the transmission. WP rapidly redesigned the Surgliator for those machines. A Maytag would have backed off on the motor carriage rollers and have suffered no harm, but it would not have done much washing either.  An old repairman/rebuilder that we used to see picking up washers from dealers told us that a Maytag was not going to do anything to hurt itself and he was right. It took a few decades for Maytag's laziness in designing washers, preying on the lack of inquisitiveness of women using them, poor management and riding on the reputation of their wringer washers to catch up to it, but we see the  denouement, or comeuppance if you will, in that the company was finally sold off.

If the old 2-belt Maytag automatic has one major fault, it's that the user can't learn to load properly it if it won't do a damn thing with the lid up.  I wouldn't say it needs to be "under loaded", I'd say that it needs to be properly loaded, and a nice full machine gets the clothes cleaner than one that's under loaded.

That said, I work in a filthy warehouse, and sometimes work on our filthy diesel trucks.  My 1972 Maytag A606 gets my work clothes as clean or cleaner than any washer I've ever had, and I've had GE Filter Flo washers, belt-drive Whirlpools, direct-drive Whirlpools, and even a Frigidaire 1-18.

There's no such thing as a perfect washing machine, they all have their advantages and disadvantages.  I've never had a Speed Queen, but from what I read on this forum, I don't think I'm missing much.