Some AB levels seem to be harder
I was going over the older AB levels, concentrating on the levels where I was the most under the average. I found that Bad Piggies has a few levels that have become much tougher, notably 21-8, 21-11 and 21-12. Reading the comments for those levels from the last two years reinforces my experience that the older strats aren't working like they used to. So maybe some levels got easier, some got harder.
OTOH, maybe (probably) after a few years of flinging your skills improve, some of the shots that were described as difficult in the comments from 2011 and 2012 are not all that tough for experienced flingers, that may explain why after a few years some levels appear easier. But if the old strats aren't working despite increased flinging dexterity, something fundamentally within the level must be different.