lucas clearly never cared enough to establish what jedi could/couldn't do in the prequels. They'd either be nigh-invincible or terry cloth soft depending on where the story needed to go. In the behind the scenes on Ep 1 he admitted he was lazy with the script and just wrote "they fight" for all the fight scenes.
I imagine the sidious fight went something like this:
lucas: ok we need to have a windu/palpatine fight here.
producer: how do we set that up?
lucas: have windu come and arrest him
producer: would windu really show up alone to face a powerful sith lord?
lucas: you're right. Let's throw in like five jedi. Make sure to get the green guy with the head thingy.
producer: so how do you plan to shoot this six-man closed quarters battle?
lucas: I'll have to get up off this chair for that won't I? Let's just kill them off in the beginning
producer: