Certainly, if you're planning on outgrowing a SQL Server you should probably DIY tailor made indexes and query languages/engines. LLVM makes DIY languages much easier to make than they used to be and very with fast interpreters and AOT it's very performant.
The reason for my brain drain statement is that people don't understand how pernicious the brain drain is in Australia. The Australian government believes that there isn't a net brain drain because more people with degrees immigrate than those emigrating. But people are not substitutable cogs and the very smart are very rare and it is the loss of those few very smart Australians to the US which is so devastating.
If you think there is a risk your database will grow to be enormous, it’s likely it’ll be the worst possible choice, with the possible exception of Oracle and DB2 on AIX (but, on the last two, at least you have fewer limits to scaling up).
Could also be a B-player hires C-players situation, with borderline incompetence trickling down from the C-level.