Yes knots are bad but sometimes they are needed. I've joined broken steering line with a fisherman's knot and it has lasted ever since (so far too lazy to join it with splices ).
In front lines knots are not acceptable. I have hard time to understand how overhand knots appear in some kiter's lines but for sure it is possible. If you are careful it should never happen. With foil kites it is practically impossible if and when lines are always connected to kite.
I've used overhand knots making bridle line loops with good results. But line is then doubled and knots have to made carefully, knot must be flawless. Figure 8 knot is better but it is bulkier and slower to do than overhand knot.
Elf kites use simple over hand knot derivative knot attaching bridle lines to loops in kite. Advantage is it is easier to remove a single bridle line than if line is attached with loop and normal method. FS LCL system is also easy but it needs LCL's.
Splices are of course best, not only for strength but usability. In very thin lines like fishing lines splices are too difficult or impossible to do, so knots have to be used.