In the big 4 defenses, black has choice and deviations galore which means white cant force you to narrow avenues if he is inclined , and many are playable. the playable non-4 defenses are a lot more narrow in their scope agaisnt critical lines and white can force black to play in a narrow bridge of few choices and sometimes even force continuations if black is to remain in the tolerably worse.
This is important because its much easier to prepare agaisnt someone if you dont have to study sideline upon sideline of options, Top players dont want repertoire's where they can be prepared agaisnt so easily. To argue that an opening has no top adherents as a primary defense misses this, its flexibility and not necessarily objectivity why this is often the deciding factor
Among not just super GMs but even IM's you will very rarely see a secondary opening or defense as a primary weapon for this reason. You become too easy to prepare agaisnt, and thats an uphill battle. But if you like 5 different things with sidelines sprinkled in, your opponent must either play chess normally, or go through encyclopediac amounts of opening prep over someone's personal repertoire to have the same effect.
You have a point. However how actually bad are the non "big 4 defenses" though?
Read the whole post. I mention both openings and endgames because the engine sux at both.
An engine needs a Powerbook to evaluate and play an opening properly!
The engine alone CANNOT DO IT!
ever heard of alphazero?
Yes I have heard of it. But it is not on the market. At least I have yet to see it sold anywhere accessible to the U.S. Amazon, Chess4Less, etc.
And yet we have Lc0 which IS stronger than A0.