But I think you're missing the point. Cruise isn't where you need more power in an underpowered twin. Takeoff is.
The most dangerous light twin flying is done from the start of the takeoff roll to whatever altitude you need to return single engine by pushing the remaining engine as hard as it can go to maintain altitude at most any airport above standard ISA atmospheric numbers and above about 4000'.
Unless you offload some weight, the second engine doesn't help much.
Lots of people are lured into thinking that second engine behaves like two on a single. Heck even on a 337 the rear one isn't as efficient.
Your examples of doors open and cowl off isn't a normal takeoff configuration *every* flight like you must plan for in a twin... one going dead and the gear still down.
That's the plan. If you get better, great... but you have to plan for the worst case. You have to fly it like it's going to try to kill you, because it will.
In a single that entails picking a landing spot.
In a twin, you add Vmc rollover to the mix and a horrendous performance hit when one stops turning. You may still need to pick a landing spot.
Here's what Vmc rollover looks like in a Queen Air:
14 dead, 20 injured. The aircraft actually came down on the proverbial elementary school that we all joke about online that the media is always concerned about with single engine off airport landings and crashes.
Only takes a few seconds of inattentiveness or forgetfulness to go splat in a twin. Just let it get too slow on a single engine.