I think instead of small vs. large (units), a distinction can be made for where a knowledge and utilization of combined-arms tactics starts to function in games.
Artillery or air strikes can literally smother skirmish scenarios – therefore, these assets are often eliminated as game components – in order to have a skirmish game.
The downside – gamers don't study or learn combined-arms tactics employed on the [real] battlefield (it's been termed as a myopic consequence of gaming style).
Member Tgunner just today posted in a thread linking a video about combined-arms tactics for Cold War-era combat -
TMP link
It discusses the recon mission, securing overwatch positions, preparatory fires/strikes, AA-cover, and concealed approaches on a battlefield (before the "main event" might even occur) – these are all tactics/elements to be fully used for success.
By their nature, skirmish games are most often just a small element of a distilled-down battlefield.
Yes, this is entertaining, legitimate wargaming, but it's a limited experience too.