My question which other people have already asked is this: why is the historical rivals modifier 'legitimate' to prevent France and Austria from allying each other, but the same can't be said for the Ottomans and Russia?
Austria and France actually DID ally each other during EU4's time frame, after the diplomatic revolution when Britain and Prussia joined forces and caused France and Austria to find common ground (Seven Year's War). Yet in game they are prevented from allying no matter what, even if one of them is an OPM or if they have the same rivals and are otherwise diplomatically isolated.
On the flip side, we have the Ottomans and Russia who were historical enemies and had severe conflicts of interest during this time period, especially with the fact that Constantinople is the center of the Orthodox Church and because both had interest in the Crimean region. The two countries still don't get along to this day, but in every single game I've played this patch, they have happily destroyed the Commonwealth, Hungary, the Balkans, and in some cases even Scandinavia together.
TLDR; if Austria and France can't be allies when they were allies historically at the end of EU4's timeframe, why can the eternal enemies Russia and the Ottomans ally each other and become unstoppable?
Also in before 'but the player can take steps to break the alliance up', yes, that's true, but the game shouldn't be balanced around the player using somewhat gamey tactics just to produce historically plausible outcomes. If I were a player inclined to role play, I wouldn't want to no-CB Byzantium at the start of every game just to prevent the Russian-Ottoman heathen alliance from dominating all of Eastern Europe and the Middle East
Austria and France actually DID ally each other during EU4's time frame, after the diplomatic revolution when Britain and Prussia joined forces and caused France and Austria to find common ground (Seven Year's War). Yet in game they are prevented from allying no matter what, even if one of them is an OPM or if they have the same rivals and are otherwise diplomatically isolated.
On the flip side, we have the Ottomans and Russia who were historical enemies and had severe conflicts of interest during this time period, especially with the fact that Constantinople is the center of the Orthodox Church and because both had interest in the Crimean region. The two countries still don't get along to this day, but in every single game I've played this patch, they have happily destroyed the Commonwealth, Hungary, the Balkans, and in some cases even Scandinavia together.
TLDR; if Austria and France can't be allies when they were allies historically at the end of EU4's timeframe, why can the eternal enemies Russia and the Ottomans ally each other and become unstoppable?
Also in before 'but the player can take steps to break the alliance up', yes, that's true, but the game shouldn't be balanced around the player using somewhat gamey tactics just to produce historically plausible outcomes. If I were a player inclined to role play, I wouldn't want to no-CB Byzantium at the start of every game just to prevent the Russian-Ottoman heathen alliance from dominating all of Eastern Europe and the Middle East