RTWP works at its best when most characters can rely on a reliable type of repeatable attack as baseline and then other abilities come in as situational to influence the outcome. It's also usually important to maintain as much clear visuals as possible.

When you have several characters and a large number of repeatable/low cooldown abilities for each one of them starts to get a bit of a mess.
When visual effects get overbearing and start to smear the entire scene and overlap each other, you get a bit of a mess.
A lot of little messes overlapping make for one gigantic clusterfuck of mess.

One of the best battle systems I experienced in this sense (while tied to a fairly mediocre game, overall) wa the one used in Aarklash Legacy.

Still, even at its absolute best I rarely consider RTWP more than decently serviceable.
It's a bit like melee combat done in first person: it can work and it can even be part of an overall excellent game, but it will never be the highlight of the show when better alternatives exist.

Party control in Baldur's Gate 3 is a complete mess that begs to be addressed. SAY NO TO THE TOILET CHAIN