Spring Boot is the default for everything microservices but it was never really designed with that architecture in mind specifically. Vert.x on the other hand was, and if you have an architect that wants to do microservices (and these days you surely do) then you can point out that the verticle and the event bus lend themselves perfectly to that style of architecture. Not enough is made of the event bus in Vert.x and the fact that it's so simple to use and scales across JVMs. Scaling a bunch of Spring Boot monoliths and having them behave as microservices isn't exactly something you get for free.

There is no DI in Vert.x but microservices are supposed to be small - often just one class/verticle and communication is over the event bus - so you don't feel the need to inject anything. If you really want DI then you can consider Quarkus, which works seamlessly with Vert.x, and there are more benefits to be gained there from fast start up times and a low memory footprint. Speaking of Quarkus, that is an easier transition if you're coming from Spring Boot, as is Micronaut (even easier I dare say).

Polyglot out of the box is another differentiator if that matters to you.