Don't know anything about the liberty, but from the couple of 'lights I've flown (sportstar / CTsw), I'd agree they're probably not as durable (fortunately not tested that), however, I think the critical bit is that they're far less forgiving, you're actually far more likely to have a heavy arrival.
Both the examples I've flown are capable of approach paths that rival / beat the old 150/flaps 40 in terms of steepness, and have relatively little inertia. They get bounced around more on approach, and are all too keen to loose energy at any point during the approach and stop very quickly during the flare. Not a problem if you can fly accurately, however the average GA trainer will let you have a bit of a balloon, or a very drawn out, gentle flare, and still have airspeed to put it on nicely. In the lighties you're very likely to find yourself 10ft up out of speed and ideas. Throw in some akward and unusual throttle locations/systems, and...
That's not to say they're bad, just different - and require some careful attention. Personally I'd be inclined to avoid for ab-initio, but it might breed sharper pilots
