Sure BJJ can be overhyped, so can striking and running away. Under ideal circumstances a quick strike followed by running is definitely best, but if you think that you can't be taken down then you're delusional, and the only way to learn to fight effectively on the ground is to practice a proper ground fighting martial art.
If someone attacks you by charging you and taking your quick strike before tackling you to the ground, then if you don't know any groundfighting based martial art, you're in a world of trouble.
Equally, if you only know grappling based martial arts, then one day you'll find someone you fail to take down for whatever reason who takes you apart with punches and kicks.
Only being able to grapple and only being able to strike are both insufficient.