Who would you rather be your captain if Janeway died, the ECH or Kim.
I'm thinking Kim would end up ruling by meeting, everyone else would basically tell him what to do. And that might work out reasonably well with everyone else including Tuvok. But all those times there wasn't time for a meeting and Kim was just utterly stumped and terrified.. might not go well.
But the ECH would do something very ill considered and ego driven when it came to crunch time and that wouldn't go well either. Still he seems to have more learning capacity so if they all didn't die during his first screw up it might kinda be okay.