Generality always lead to caveats, but he is talking about for physical existence and in sports absolute strength is the key element for success and longevity in both sport and life...I've never read any Riptoe or listened to any of his programs. Unless I misread it, the quote said that physical strength is the most important thing in life, with no qualification that he was actually talking about sports. That would be less insane and stupid, but still demonstrably false, except for sports like powerlifting. I'd much rather be a great surfer or fighter than a great powerlifter. Strength is certainly important in surfing and fighting but far from the most important thing. Having a typical powerlifter's body would actually be a disadvantage in surfing and arguably also in many types of fighting.
This mentality is what the dynamo club in Soviet Russia believed also when the took their athletes and developed the conjugate system. (Not what Rip does at all)
Strength and weight gain are not the same. Strength display is a product of neural efficiency combined with muscle mass and technique. Regarding fighting... All of the MMA guys train, many use a conjugate system, but ALL of them weight train.
Strength is measured in velocity.
Of course having a 900 lb squat doesn't mean you'll be a great boxer, but it does mean you'll be able to have better neural effeicencyfor delivering punches provided you have the technique
If you put 11 strong kids on the field who are playing Football and all of them can deadlift 500 and put 11 weak kids on the field who all deadlift 225, the 225 team is gonna get smashed.
So yes, strength is not a factor in Chess... But its importance in sport and physical display is what determines the top provided that technique is sound.