Start time is not a great measure of overall performance. Also you are comparing two very different types of applications.
A text editor that can be extended vs a platform application is the same argument we've been having about vim vs emacs for years.
DBeaver is an incredibly powerful application that had allowed me to work in Postgres, Teradata, and Oracle databases for years. Could I do the same kind of work in VSCode? Absolutely not, unless I wanted to build out an entirely new interface on top of VSCode. By the time that work is done it could be equally slow to start up. DBeaver has an absolutely massive feature set tailored for database work and it has to load all those plugins at some point.
Another counter point is VSCode with java-lsp could never handle the 300k loc code base we developed on, where intelij and eclipse do just fine. Yes, they startup slowly, but at least they provided meaningful and fast autocomplete without the need to wait for the language sever or VScode to unfreeze.
Again these are purely anecdote, but please don't purely judge an application by it's startup time if it saves you time in the end.