It's not a "size" confirmation, it's a confirmation of all the details of the update, including warnings about ignored packages, and the full list of updates (potentially the list of updates provided by VerbosePkgLists).

For fully automated scripting use, you may be interested in https://github.com/andrewgregory/pacutils/blob/master/doc/pactrans.pod#prompt-disposition-options

I'm not sure it makes sense to offer a noconfirm option that actually does make you confirm things, since that would cause Pacman to block on input rather than failing gracefully in a way that can be caught via the exit code.

I think there should be an option similar to --noconfirm, that auto-confirms the things that aren't "real problems", but asks for confirmation or exits if it encounters a "real problem", like conflicting packages.
Because those prompts for "no real problems" make scripting kind of a nightmare.

Again, if you want actual scripting support, why not use pacutils?

Pacman doesn't really offer a guarantee that it's suitable for scripting, and we've historically been very reluctant to do much work in that regard.