IMO almost nobody is writing microservices with spring boot because its so gigantic. Hibernate isn't bad on memory use on its own.
There's a raft of more sane choices these days like Play, Dropwizard, Vert.X etc.. They all use far less resources. Spring Boot is huge because it has to support a decade of obsolete junk, its far more than just a REST app framework.
>IMO almost nobody is writing microservices with spring boot because its so gigantic.
I've encountered plenty of spring boot microservices in my work and, from what I hear of other companies, it's not particularly rare.
Most of the time, if you have a team that's productive in Spring, a manager or lead will be happy to spend some extra memory and get more features shipped.
So you actually haven't tried to run an application with those libraries, and you don't even know what libraries that particular application is using, and here you are speculating about something you don't know and/or understand.
I've used Spring and he's probably right :) . But there's better choices these days. Any Spring micro-services out there are probably by a team that knew Spring well and didn't want to learn a more suitable framework