ETF is just a very important tool for more Bitcoin adoption.
Care to elaborate how an ETF helps on adoption? To me it rather seems as a tool for investors to not care about custody and regulation. It's just a little better than Binance's BTC IOU.
The worst thing these corporations could do is convince Bitcoin Core devs to argue about every soft fork so that Bitcoin is ossified and cannot scale.
You make it sound worse than it should. If corporations manage to persuade Bitcoin Core developers to adopt a specific roadmap, they would likely succeed in convincing the broader community of its merit. In the event that Core developers receive compensation for a hard fork, they would need to persuade others to embrace the fork, not just themselves.