After a claim that casters get to rest after every encounter it's hard to take that anecdotal take seriously.
I usually run my own campaign, but lately I've run both the Spelljammer adventure and the Planescape adventure.
In both, the great majority of the time, the group gets to long rest after 1 sometimes 2 encounters. This greatly favors the casters because they can unleash their high level, often encounter ending spells, much more easily.