You would only need that much if the tubing was tapered at a pretty shallow angle, to make you feel confident.. You don't need that much strength, and if you do need that much strength then you should be using different tubing in the first place. No lap joint is going to save you from the wrong selection of chassis materials.
It just doesn't make sense to have the lap joint be many times stronger in bending than the tubing itself, it isn't necessary. Steel is cheap, welding is cheap, so who cares, but don't fool yourself into thinking it's necessary.
If you tie a knot in a rope, and the knot is 30 times stronger than the rope, you haven't improved anything over a knot that's 3 times stronger than the rope. Either way, the rope will fail before the knot so making the knot 10 times stronger gains you exactly nothing. Yes, I know you probably can't make a knot that strong, it's just an example for illustration...
