For sure a 40 ATK 4 DEF build is faaaaaar more useful than a 4 ATK 40 DEF build; but you wouldn't find me running either. Sometimes you just can't help but take a hit, so all attack builds are hella risky.
About the ratio in general, yep, attack is generally more powerful than defence. I've come to think of this as a positive though, if the two were balanced the answer to "which do I want more of?" would always be "which do I have least of"; this way, you need to decide how much more valuable ATK is to DEF for you.