[...]
It very much depends on what you (honestly) care about.
If you do not care about readability of the programs you write, then it is "tooling issue"
(like in "Use Merlin bro!")
If you care about readability, then ephemeral Merlin (or whatever) tooltips are not exactly the same stuff
as type information that is directly, permanently, unconditionally present in the source code.
From the reader's point of view, it is not the same thing, really.
In addition to that, when one uses polymorphic variants heavily,
the presence or absence of typing annotations makes a drastic impact on the ability of typing errors the compiler can generate.