The problem I've experienced with the LEDs is not that they burn out, but that they output less and less light as time goes on. As an example we outfitted a gas station canopy with LED lights a year ago. When it was first done and I drove by at night I was impressed with the light output. It was as good as, if not better than the mercury vapor lamps they replaced. Now only a year later with the arrays on about 12 hours a day I think it would be safe to say they have dimmed by 25%-35%. None of the lights have failed and none of the LEDs in the arrays appear to be out, but they all seemed to have dimmed equally. I'm not sure how much dimming of the LEDs constitutes a failure, but IMO if these arrays dim any further they will need to be replaced as the canopy lighting is now toward the low end of acceptable.
Have you done a lux meter comparision of a new set with one that has been in service for a year or two? I've used a simple one to determine warm up time on CFL's. By comparing a spare or new-in-box sample of the same model you could verify your impression. If you think they have dimmed by 25-35% visually, then they've likely dimmed by far more than that. You would be amazed at how little light some CFL's start up with when cold (room temp) vs. their normal output 1-2 minutes later. They can look perhaps half as bright but instead be putting out 1/8th as much light.
I'm surprised to hear of this LED dimming problem as the CFL backlight in LCD TV's is supposed to be a problem over the long haul since it dims and shifts color spectrum over time. Supposedly LED TV's won't have this limitation.
I also have more CFLs inside. In an open air fixture the bulbs last forever. In the bathroom they last about as long as a regular bulb, maybe a little less. In a closed fixture they die within 6 months. I have not tried the CFLs designed to go into recessed lights and don't plan to as I would miss not being able to properly dim my lights.
I haven't experienced premature CFL deaths in either of these two scenarios, fortunately. (It could be a brand thing I suppose.) I've got at least 8 CFL's in closed fixtures indoors at present and haven't lost any of them that I can recall (3.5 years in this home.) I did have some early GE failures in another home and I think some were enclosed, but the GE's seemed to fail earlier wherever they were which is one of the many reasons why I haven't bought them in years.
I've got plenty of CFL's in open fixtures in bathrooms, roughly two dozen. I've lost at least one, perhaps two in ~3 years...but some of these had been in other homes for years before this.
CFL's have severe dimming when used outdoors in winter (and there are some temp limitations on them.) Still, I have some of the enclosed R30/R20 types in cans outside. I don't use them much but I haven't had a failure. I've also got some standard CFL's in enclosed and non-enclosed fixtures outdoors, plus 4 in garage door openers. The garage door opener ones have done well as temps there are more moderate.