Yes.. LED light output does degrade over time. Its well known in the sign trade where LED has become the dominant light source for backlit signs. If you have them on say 8hrs a day then expect them to drop back in under 3 months.
Please note that the wording on life expectancy of any LED has been changed from 50,000hrs to UP TO 50,000hrs.. this is the best case scenario and dependent on the style of LED.
Also, an LED warranty isn't quite what you would expect from any other product. LED is only considered faulty by the manufacturer if it is working UNDER 60% of its lumen output, so your cheap LED stick down strip can have 35% of the LEDs drop out and it is still considered a fully working product and it may well sit like that for 10,000...20,000hrs etc... looks like crap but still good according to the manufacturers.
If you believed you bought a source of light that will never need replacing then you have to ask yourself why a Chinese manufacturer would sell you something that will ultimately put them out of business.
50,000 hrs is laboratory conditions.. the only light source to consistently prove OVER 50,000hrs in the field is neon and cold cathode which have also been given the "Green tick" by UL as the greenest form of lighting due to its low power consumption, high lumen output and its ability to be recycled.
OK.. so you are not going to put neon lamps in a pinball but you do need to look beyond the hype of LED and deal with the facts.

50/50 requires 3X the current a 3528 does

They were certainly touted within the sign industry and having to never be replaced and the claims of lasting 20,000 or 50,000hrs have changed to "up to".
I was bringing constant current LEDs into my country some 8 or 9 years back and the quality was good. My manufacturer later emailed me with concerns that as the push for more and more product to meet demand came, the quality would drop and many of the benefits of LED would disappear. Interestingly, that company no longer operates.
But as a side note.. my 1930's and 1940's pins I have still have the original incandescent bulbs in them and they all work.. my 1937 Stoner Ricochet was sited in a milk bar for 20 years and then went into a home environment. So there was a time when incandescent lighting was incredibly reliable... food for thought.