I think the trigger needed for intervine in a war with this mechanic would be 3GP vs 1GP or simply delete this diplomatic action, otherwise a balanced war like Spain, Portugal (GP) vs France and allies, could be broken by Ottomans entering war with France.
In my case, me and my allies (colonial nations included) have around 150k infantry, France, Bohemia, Brandenburg and allies were around 160k infantry, then Ottoman Empire joined the war with France, so they have now around 250k infantry, fairly unbalanced, now I know i will lost this war.
But not the first time in this match. Twice times I was called by Austria cause Im his ally, against some countries, Papal states, Genoa, Venice... It was an early war, and it was balanced, I sent my troops trough France, atm i had military access and +150 relations with them, but when I arrived Genoa, France joined the war as GP and I got my troops stuck in Genoa. I solved this situation by early white peace, but my ally get ass kicked the two times.
So, I was forced to broke my alliance with Austria.
I would like if anyone knows how to mod this... because this mechanic are ruining my game