The most thing with impressiv me a lot was how casually Grindelwald was using a spell who was capable to destroy Paris and how much aurors get take out by it. It take Nicolas flamel and other strong fighters to match up his spell, Nicolas flamel and many aurors would be a dangerous threat for Voldemort, overall he fear a battle with Dumbledore even though Dumble was far away from his prime power.
About Dumbledore vs Voldemort, one side has good arguments, Dumbledore didn´t try to kill him and even less then his prime he was able to pummel Voldemort who leave the battlefield because of fear. Also their is a speculation that Dumbledore couldn´t and didn´t want to kill Volde because he know about the Horcruxes. Other side has also a good point with saying Dumbledore had the Elder wand with make Dumbledore far stronger.
Overall Dumbledore was out of his prime(probably even with the Elder Wand he wasn´t strong as his prime version who take out a wizard who also had the elder wand), he protect Harry during the battle because Voldemort target Harry multipletimes and he didn´t want kill Voldemort. In that case we can agree that Voldemort would get beat down even by the older Dumbledore.
The case is that the prime Dumbledore who be said beeing far stronger by Dumbledore himself, take out the strongest wizard+elder wand with make it clear that Dumbledore in prime was a monster. His duell with Grindelwald was said to the most best battle in the history of the Wizard which take three full hours.
For now something telling me that Grindelwald would take this battle, Voldemort make too much mistakes(use always the dumb curse spell who never work against Harry rather then using a another strong spell) and his tactic as wizard wasn´t also great, everytime when we see him in a duell he was outclassed by either Harry or Dumbledore while Grindelwald is a extrem good wizard who can control his feeling and have a great skillmove, he stay always calm down while Voldemort lose complete the focus because of the anger in him. Because that I see Grindelwald little above him, however probably the next movie answer more for Grindelwald feats.
Rayan you though for the most 10 strongest wizard in Harry potter verse?
In the end I agree that Grindy can take it because Tom personality is up and down, he can be really really smart or dumb, can be a perfect planer or be fooled, ban be collected and cunning or full rage and tantrum, is afraid of death like nobody else etc.
Grindy can use that to beat him but magic wise I have my doubt. Voldemort was always named as the strongest and he did things magic wise that nobody managed to do before him.
I really think that Tom had the best potential of all. He really ruined it.
And to be fair I also doubt that Dumby wanted to kill Grindy too during their fight. The guy was mad in love with him.
Grindy managed to cause havoc in all Europe but because Dumby didn't want to fight him directly. Voldy began with the hardest country where the big boys were : Britain. And Voldy was doomed by Harry because of some prophecy and special magic curse. Without Lily love who knows what Prime Voldy could have done.
About the 10 strongest in HP verses : I would only talk about the times we really know about so no founders or Merlin or some older goblin kings lol.
So about the 20 centuries wizards :
the top 3 is quite easy :
Dumby
Voldy
Grindy
Those three are clearly a level above everyone by head and shoulders and can tale multiple fighters at the same time after them in this top 10.
After them we have a group of very powerful guys but somewhat close to each other :
Snape/Bella/Alastor/Mcgo
Amelia Bones was also killed personally by Voldy and was not a pushover.
We also have the like of Sirius or Kingsley. James and Lily were said to be quite powerful too in their days.
Slughorn is not a weak wizard too : he fought Voldy with Mcgo and kingsley in the last book. He was beaten but this is already a good feat and even Lucius Malfoy said that Horace was a good wizard and the guy doesn't have the easy praising.
We also have Croupton Sr who was said to send powerful curses too.
There is also Flitwick who is a master duelist, clever and has a lot of knowledge.
But I think after the big three : Snape, Bella and Alastor are the best. Snape has an insane potential and was a gret duelist. Also knowledgeable in many magic fields. And he was young. Alastor is top auror and Bella managed to block one spell from Dumby, Voldy taught her some magic personally too.
After : Mcgo/Flitwick maybe Bones, maybe Sirius.
After : Slug, Croupton, Kingsley
but my rating is maybe not perfect and maybe I forgot a lot of characters.
Yes Fawkes ate a killing curse but that’s part of Dumbledore’s tools.
We can said the same about Nagini but she wasn't there.