The AI behavior has not been changed, so anything you're seeing is a result of standard mechanics. The different ideology opinion penalty is 0 and the US and Australia have several opinion buffs in the mod. I will be reducing the AI reluctance to join wars from economic law but democracies will always be less likely to join offensive wars. The AI will almost always join your wars if they are in your faction and the situation suits their interests. Reducing the faction world tension requirement would make conquest more difficult early on because the AI will ally when you go to war with them.

If you want to work with other countries as a modern empire, you will need to choose an undemocratic ideology and flip theirs to be compliant. Playing an offensive democracy will almost always be a solo journey unless you can manage to ally with undemocratic nations.

If you are concerned about faction tension requirements for multiplayer, you can use the "Spread Warmongering Sentiment" decision to reduce it by 40%. If both players do this, they should be able to join up.

I agree with your points above and to be fair it is quite realistic because Democracies are less aggressive than other types of governments for sure.

I mainly put my post up to hear how other people play as Democracies to swap strategies and tactics between each other.

I am getting the vibe you should only join a war if you get dragged into one and stay peaceful trying to develop your alliances. Once you are in the fight it is a lot harder to add allies.