Everyone has been poking around the edges, but I don't think I saw my exact take yet: The key to this is to be
brutal about separating the player versus character linkage.
As was already stated, from the player perspective the important thing is that all the players be engaged in the action. You can do that several ways, but the most obvious is to make sure:
1. That a player doesn't have to wait too long to make a decision.
2. That what other players do is interesting (as roleplaying, or tactics, or even mechanically) to the other players.
Note that while gamism, simulationism, simply paying attention, group needs, etc. all enter into that, none of them are as decisive as the players' preferences. (If I think I have to wait "too long" to make a decision, I think that, independent of what others may have achieved in their group or the particular form of the gaming.) However, you can please everyone (on this point). Or at least almost everyone.
From the character perspective, you want the rules to make some kind of sense. Could be a gamist sense. Could be narrative sense. Could be something else. Again, it depends on the players, but here you can't please everyone. For example, it may very well be that the druid has a summoned bear, the ranger has a wolf companion, and the whole party hired three mercenaries. If you go the "one action per player" route, you'll satisfy one crowd (sort of), and not the rest. If you say, "play it out, the same way you always did", then ditto. Likewise, "Make followers incompetent or fluff". They only work for some people, because those are kludges.
So back to that brutal divide. There are two kinds of groups, with two different answers to the divide:
1. Groups that have decided that sticking with their character perspective is more important than other considerations are free to use those kludges, same as they always have. It should be acceptable, since the main thing is focusing on their PC. They categorically reject the brutal divide, but that's OK. We don't need any special rules for them.
2. Groups that have decided they want multiple characters controlled by players have already accepted the divide. So give them tools to embrace it. For example, specifically reject the idea that a cohort bought by a feat is controlled by the player of the character that spent the feat. You buy a cohort for your character, which any warm body at the table can then play (including you), as necessary. Same with summoned creatures, hirelings, whatever. Heck, it need not even be the same player handling them from one scene to the next. While you are at it, throw a few neutral NPCs or even foes into the players' laps. After all, the point is to keep the
players engaged.
Economy of actions has (of course) repercussions for the characters, but it only truly matters for the players. Don't try to solve a player issue with a character mechanism.
If I went long with this, it may only be because of some homebrew design work that goes fairly far afield handling the second option.
