Maybe I missed something, but I received my new 2-player core set yesterday and played through the first quest and noticed something different from "first edition." From the learn to play rules (also posted on the FFG page, dated 26 JUL 2018), I don't see any reference to exhausting in order to attack. The Rules Reference (dated 29 MAR 2018) still notes that attackers are exhausted.

So which is it? Do characters no longer exhaust in order to attack, as per the later dated learn to play rules, or is this a typo? If characters, in fact, do not exhaust to attack, is there anything that keeps a single heavy hitter from attacking every enemy engaged with a player?

Seems like an oversight in the LTP rules. Page 19 of the LTP book still shows attackers being exhausted, and in general the Rules References always override Learn To Plays.