Agreed, but I think Plausible differentiates between sessions and visitors? The term should be sessions: non-unique visits across a defined time range. At least that is what I do with Pirsch [0] and on my website [1].
We don't show the number sessions/visits at the moment. Most seem happy with the 'unique visitors' number and we don't want to add extra data to the UI unless it's truly useful.
If you want that, I suppose GA or Matomo are for you? Has to be something to differentiate them, pointless to expect or want them all to be the same.