If you really figure that LEI's depower more than foils that you obviously haven't kited a good foil that was designed in the last 4-5 years OR the foil you kited with was a crappy design (usually the cheaper brands/models out there => terrible design/ crap performance....what a bargain!).
For best progression, to sum up:
LEI's => Water and snow use
Open-cell foils => Land and advanced snowkiting use
Who ever doesn't understand this hasn't spent enough time on a good foil kite while snowkiting or kite-landboarding (not just on an open beach).
Though I agree with some of your statements. Some I don't.
Depower foils are slower with less depower at the bar than the equivalent lei size. When opereated in their wind range are awesome kites. They are more powerfull generally size for size. But have some entrained power still in them when you let the bar out when moving.
Recently I was kite buggying in sand dunes. Ok slightly different to snow kiting. but the same theories apply when kiting terrain. On one day I flew 15m speed 3 closed cell, 13m ozone edge lei, 10m ozone c4, and brand new 2014 12m ozone summit open cell foil. It was a good comparison between the 3 styles of kites
To my suprise i enjoyed the flight charactersitics of the leis more! this is a shock to me as i'm a die hard foil fan.
But the fact is the foils don't depower as much at the bar. I could let the bar out on the lie and easily safely trundle to the bottle of the hill without fear of being lofted or over powered. I could crank a high up wind line going upwind down hill. The faster lei was more fun to throw around and react to the terrain in front of me.
In fact I experienced a "death run" down one slope on the 12m summit. I just couldn't shut the power down on the summit and ended up cranking down this slow at high speed. The exact same slope on the 13m edge was easy to navigate. let the bar out and cruise down.
easy launch and land, smooth powered delivery. dont need to pump. more compact and can carry spare kites. generally good float and less need for a perfect redirect.
worse in turbulent rotor conditions, smaller wind range.
Open cells collapse more in in gusty conditions that closed cell. closed cell have better slack line capability. But are more powered on the brakes when landed. Flag out safety on closed cell foils kills the power as much as open cell.
faster more, depower, more stable in turbulent conditions. best slack line/drift capability.
harder to solo launch, less robust, needs pumping harder to take spare kite.
Lastly. ride what you are used to. If you are not used to foils and ride leis 99% of the time then you will hate the foil.
But want to do back country riding? then you need to get into foils for the ease if pack up/set up and the safety of being able to take a spare kite with you.