Feldman had some initial success for about 5 years following Goonies, before the burnout
It's just that Astin has had the bigger long term career, albeit with only two real defining roles beyond Mikey (Rudy and Samwise)
Though that's only if you limit it to the kids and exclude Davi and Pantoliano, who've had decent careers since.
Toy Soldiers.
Great movie, but not a defining role character
The three characters I said are the ones (so far) that he will be remembered for... first for Samwise, because it's the most recent epic and freshest in people's minds, then for Rudy, because it's a legendary film, and then Mikey