If the problem to solve is getting shy players to take initiative and people feeling welcome to participate in mixed scenes then honestly I don't think that is ever solvable by system or mechanics.
That is a game culture thing.
You can nerf everyone into oblivion, remove whole systems from play and you will still have players who have anxiety about jumping in because it is not about sheets but initiating out joining play. You will also always have players who will refuse to participate in anything they're not "good" at and define being good as having a high probability of success. There isn't anything wrong with that as a playstyle but in that case nothing will really satisfy except for free-form play with no risk, so if they need that to feel comfortable and welcome then honestly they'll need to find a game that allows full choice rather than systems that allow for failure/risk.
And again, those games can be fun too esp when there's a culture of sharing the limelight and interest in developing other people's stories.
The issues tend to happen when there are mixed playstyles/expectations. People who enjoy risk of failure/less control over degree of success and needing to adjust play accordingly are going to see a system as a means to help them enjoy that kind of informing of play. If others see it more as a guideline to inform their play in general but not limiting it to whats on their sheet, thats going to clash.
And even then you have differing personality types (such as the all or nothing folks, if they are you maxed out or high statted for a thing they don't feel comfortable even trying, or someone moving from a high xp/power game to a low or moderate one now feeling inadequate).
But I think it is almost never the system but game culture. And you must cultivate the culture too, the system won't build it for you. Without guidance, you'll still have people not on the same page but hundreds of them.