I disagree that the Chargers gave Herbert a "bad supporting cast". They actually did everything possible to give him a complete offense. Their skill players are definitely above average as a while. The offensive line was rated in the top 10 by PFF going into this season.
They have severely underperformed.
Did they really? Keenan is great, but that’s just 1 guy & he’s getting older.
Ekeler is a one trick pony.
Mike Williams stays injured & is a jump-ball receiver.
Quentin Johnston….the less said about him, the better.
Josh Palmer is okay for what he is.
Outside of Palmer, they gave him a bunch of slow ass WRs.
The TEs are meh.
The OLine is mediocre.
Herbert could have played better, sure, but supporting cast always had a low ceiling at best.