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 hardfork, they would need to persuade others to embrace the fork, not just themselves.
I can imagine a scenario where there is a contentious MASF, and popular Core developers insist this is an attack on Bitcoin. Economic nodes like Coinbase could attempt a new idea called a User Rejected Soft Fork (URSF) that will invalidateblock any blocks with upgraded transactions.
While a URSF is
called a soft fork, it is actually a hard fork because it breaks the heaviest chain rule. Then suppose Core officially releases a
real soft fork update, without the code from the other soft fork. This is still a hard fork.
The nodes that never updated have already confirmed the blocks, so any attempt to block a soft fork with 51% hash power is always a hard fork.
BlackRock says if there is a fork, they will decide for themselves which is the
real Bitcoin. So imagine one soft fork gives us global scalability and privacy, but BlackRock wants an expensive rock that does nothing. While I don’t think BlackRock could single handily crash Bitcoin’s price, they could choose the rock and adequately effect the price enough to invoke fear.