Any research or data analysis that shows how centralized Polygon really is?

A standard critique is "it's a centralized sidechain" but I haven't seen anything published that shows how it is more centralized vs other L2s

Simple explanation:

Polygon PoS is a blockchain secured by 100 validators. It derives no security from Ethereum or any other chain.

I work for Ethereum at the Ethereum Foundation.

L2s derive security from another chain like Ethereum. Ethereum is used to keep verifier records of what happens on the L2, like insurance. 

Most L2s don't have every piece of that insurance finished, but many are close. 

Polygon PoS has no similar "Insurance"

understood re: underlying L1 security, but what about decentralization? aren't L2s such as Starkware or Optimism currently as centralized as Polygon?

"decentralization" is a very fuzzy concept here. In blockchains we're often using it to gesture at a number of different properties a blockchain or application might have, but it doesn't have a precise meaning outside of very specific contexts.