I really don't understand why some people find the traditional method to be a good challenge.I hate catching legendaries. I'd rather the fight be hard but a guarantee catch when defeated (aka you proving your worth) vs throwing balls until one works or i soft reset and do the same thing again. Its why i highly prefer the dmax dens than anything else
Challenge? It's way too easy to put the legendary into a non-threatening state, at 1 HP, paralyzed/asleep and unable to deal enough damage. The only "challenge" is begging the RNG to think it's a good idea to catch the Pokémon, instead of waiting until it KOes itself through Struggle.
The D-Max Legendaries provide an actual challenge, without an incredibly low catch rate.