I think a good way to revamp Ares would be for it to come out that he and Steve Trevor are like two sides of the same coin but unaware of it. Like a Jekyll and Hyde type scenario. I like this idea because Wonder Woman claims to be a champion of love and an enemy of war yet she's a warrior by nature and I'd love for a story line that calls her out on it. Like Ares is seemingly killed Diana is about to marry Steve Trevor all is right with the world then just as they say "I do" and are about to kiss the wedding is attacked and then during the battle Steve starts going through a weird transformation and he doesn't understand what's happening and boom he's clad in black armor and the once thought vanquished Ares returns and it's discovered he and Steve Trevor are two parts of the same whole.
As for how I'd do Ares's origin I'd have written that a lazy Zeus and Hera not wanting to bother with their child abandoned him(there are many myths of Gods abandoning their children) in the world of man during a harsh and violent time of man kind's history and for Ares to have lived a life as a slave, then gladiator, then an honored soldier and for him in the beginning he could have been a good man who had faith in the gods much like Diana believes in her deities only as soon as he discovered he was a god among mortals he discovered to his horror how the gods he spent his life having faith in really didn't give a **** about humanity. Which would cause him to look back on all the sacrifices he made and feel nothing but disgust for himself and humanity because he'd feel like a fool for believing the world of man was worth saving and fighting for. Then when he began training Diana (I think I read somewhere he trained her at one time) he saw a lot of who he used to be in her and couldn't handle it so he pushed her away and subconsciously created Steve Trevor as a coping mechanism.
Pretty much with Ares I'd make him someone who used to have faith and used to care for others then just stopped caring after losing everything while discovering the truth about himself and just decided to just drown himself in battle to numb himself to his own pain. What I like about this is it really creates a chicken and egg conundrum with Ares like is he the God of War because he was meant to be or is he the god or war because he was influenced by humanity? Pretty much someone like this warning this clip is graphic.
Now with Cheetah what I'd do differently is I'd reboot her past so that when Diana left her home something happened and she lost her memory and got taken advantage of by mercanaries and while working for or with said mercenaries Cheetah's family was taken hostage and Cheetah begged for mercy from Diana who at the time had no memory of her past and so the worst scenario happened and Cheetah lost her husband and children and later found herself cursed and transformed vowing to take revenge on Diana. I like this idea because it really gives Cheetah a deeply personal reason to hate Diana and leaves no hope of them ever being able to reconcile and at the same time it gives Diana reason to keep trying to appeal to Cheetah's humanity.
Finally Medusa I'd retcon her as being Hypolita's first born daughter and a amazon that was a victim of the god's cruelty(especially Poseidon) and that instead of protecting and believing Medusa Hypolita shunned her and sided with gods choosing instead to not anger the God's wrath and I'd also retcon the Gorgon's as a tribe of Amazons that were banished and shunned like Medusa for defending and taking Medusa's side. I like this idea because it really makes Medusa a villain to root for. I like this idea because it makes Medusa a good tragic villain and gives her plenty of reasons to hate the Amazons.