I think you could email them to rethink whether short-lived things are in general a good idea with regards to a) performance b) maintainability/overseeability/debuggability/flexibility.
IMHO short-lived by default is a wrong practice, and it's mostly a consequence of the misaplied ideology that everything should have as tiny a lexical scope as possible (e.g. make stack variables where possible). And it's a consequence of OOP thinking, where there isn't really a concept of "memory you can use when you need it" but only "objects that are always constructed". And whenever an object comes into or out of existence, work must be done to make that transition official!
If matters were as simple as using SSO vectors by default (or almost always), then new languages would choose SSO optimized datastructures almost everywhere. But is it actually the case that almost all data fits in arrays of length < 16 or so? I don't think so, and using SSO data structures causes more complicated object code and is slower in the larger cases.