The issue with making all stats equally useful remains that people only get X points per level, and encouraging everyone to spread their stats around just produces a party in which everyone has pretty much same stats as every other member despite having different weapons and attack styles.
No.
If there's only one stat useful for a given character, than having a stat system at all is meaningless, since you effectively scale everything with level anyway.
Making each stat do a different but useful thing for every class is exactly what justifies having a variety of stats in the first place: it produces a variety of results.
You'll always want to focus on something in particular, but there should be hard and meaningful choices to make outside of your primary attribute at the very least, and right now Original Sin 2 offers only no-brainer non-choices, which are a major step back from the original game.
