That image is greatly misleading. (This will be also response for your question)
Old Gods were powerful, posessed magical powers, wisdom etc. But they still had mortal flaws. They made errors, could be beaten and die. We have stories about men, who have challenged or even become Gods. Gods could be angry to men, but also men could be angry to Gods. You can abandon and defy them (not good idea tho). Gods held lots of power and could help or harm, but the man still chose and made his destiny.
Abrahamic God however is omnipotent, cannot be challenged, is always right, and always win. Even created the world. That is not something you can relate to. All you can do is to submit, he has decided everything for you and there is nothing you can do about it.
Second thing. Which one sounds more legit religion>Some random dude on the other side of the known world said that this God is the real one, and we should submit or die
or>Beliefs that your ancestors have had that date back in the origins of time
The problem with "legitimacy" of christianity, is that is all is based on one guy (or small group) of people to telling others that "I'm the son of only true God, do as I say". Comparing old religions with christianity is little like you would be now asked "Would you choose to belive in christianity that dates back millenias or this random guy from the middle-east who claims he is the son of only true God?"
I hope I got my thoughts out clearly enough.