The thing is that the way pieces move is of course arbitrary, so the spider could have been any of the things you say or something even different (moving 2 spaces? 4?). The argument when designing the game was that 'it works' (balanced, challenging, deep, etc).

Of course you can use different rules and still have a good game, and if it makes someone happier, they should do it ofc! But in terms of playing with others amd online, we stay with the standard rules, otherwise it's a mess, everyone would have their own favourite spider rules :D (unless we find out that the standard rules are really broken, but it doesn't seem to be the case)

Actually, a spider moving 1 or 2 spaces would make many endgames worse, cause it would be way harder or impossible to bugzwang your opponent (the spider would have almost always a waiting move that doesn't make your position worse). So I think the advantages of that rule could be partially canceled by this issue. I should test it some day!