Can there even be war if the opening move is devastating enough? Any conflict would devolve into the long clean up rather than any serious affair.
Insurgents are a pest, but they are one that can ultimately be ignored at the global scale.
Mathematics for numbers of muggles versus number of wizards.
My suburban city has 60,000 people living in it, and of those, about 4,500 are in high school, and 1,000 are in middle school (essentially years one through seven)
That's 5,500 of the population (9% of the population)
At Hogwarts, according to visuals from the movies, because all we have is a number that J.K pulled out of her arse. At each table, there are approximately 4 people per bench, and about 30 benches per side of table. In total, there are 320 benches. So there are 1,280 students at Hogwarts School of Witchcraft and Wizardry.
Use that to find the total population of Magical Britain.
There are 12,940 or so wizards and witches in Magical Britain, which makes sense. There is only one school in ALL of Britain in canon, and that means a lot, because even my suburban city has three different high schools and three different middle schools.
Now let's look at the population of Muggle Britain in 1981
56.33
Not thousand, not hundreds of thousand, but million
The Wizarding world's population is 0.00022900763% of the total population of Britain
The size of the uk's military in 1981 was 333,800 personnel.
If the path of Grindelwald is followed, the extermination and enslavement of Muggles must follow, for that is what the Greater Good was. It was unifying the magical beings against the tyrannical muggles who outnumber the Wizards by so much that even the Russians of WWII would be jealous of how many bodies they can throw at you. I shall not even continue on and mention technology. The more in detail I go, the more impossible it becomes.
Edit: Again, I'm just clearing up some things I noticed. You can't just have the "Magic is Magic" part of Grindelwald. You also get the "Muggles are evil" part of him.
If you want a philosophy simply based on "All magicals are equal" go for the Old Ways. That's the path where you'll be able to unify all magicals without declaring war on the muggles. Really, it's more of a Greater Good than the actual Greater Good philosophy.