Big banks are invested in most major coins now and especially Bitcoin Legacy/the implementation of supposed "Bitcoin" developed by Core team.
Investment alone is not meaningful to attack as "centralization". Satoshi wanted investment and he wanted miner specialization. He did not however want a developer team to ignore his vision as he had clearly expressed it in print.
It's the incentives in Bitcoin (as per the whitepaper, in now in Bitcoin Cash that is, which still retains these incentives untainted by the developers) that makes it secure and viable as a global money.
-Just to answer your worst concerns however, even if there was a 50% attack this could be limited and even if limiting it was unsuccessful we could still fork.
It's also a mute point who markets it. I could be the best or most well known marketer of Bitcoin one day. Up until recently (when it diverged from Satoshis white paper) Roger was the most prolific marketer of the "older" Bitcoin brand. Does any of this make it "centralized" in the truly meaningful sense of having control of what happens to individual users funds? The answer is clearly no.