During some valid clinch, the striking won't be effective at that moment.
In those pictures I can see several very good strikes the guy in the headlock can use.
But all take down are effective take downs.
Not really, in MMA to be effective ie scoring you have to do something with them, a takedown itself won't score, it's what you do after that counts so no not all takedowns are effective. If you were to takedown your opponent then lay and pray that's not effective nor is it effective if your opponent takes control or gets back up.
Once you are on the floor, striking can be very effective even devastating, you have fists, knees and elbows, hammer fists are nasty.