What’s the point of Physick for Summoner?

[Exodus-E]

From a lore standpoint, red mages heal and resurrect because they use a combination of spells associated with white magick (healer) and black magic (casters). Summoner has no such lore.

Don't like how Physick works? Don't put it on your hot bar.

From a lore standpoint, Red Mages use a combination of (present-day) conjury and thaumaturgy.
They don't use actual white magick or black magick, as their practice has been "forbidden" (and/or available only to a select few).

As for Summoners being able to use Physick and Resurrection, it's because of Arcanist (integrating Summoner's knowledge into its repertoire).
As simple as that.