SME and IC are functionally different. SME informs, IC creates. Often, IC aren't SME in the space they're developing in, because they're SME of the technology instead of the business.
This whole thing reminds me why I never wanna work for someone again. From what I saw at Google it all just ends up being classist top-down BS of who isn't allowed at the big kids table, or bottom-up BS by insisting they aren't the SME just the IC and we can't do anything until the XYZ PM SME TL and/or manager approve.
It is unparsable Dilbert nonsense to anyone outside of specific scenarios. And it causes interminable discontent. Because what if the SME is the PM because they know business and tech but the SME is actually the IC because they know the tech and its tech but what if the manager is actually the SME because they're running the tech and may need to redelegate if the IC needs vacation, blah blah blah.
(job history: college dropout waiter => my own startup, sold => Google for 8 years => my own startup)
I agree that technologists are SME of their field (so we still call them SME in my Corp)