Well, yes. But consider the opposite case: the company doesn't prohibit these kinds of passwords, and the attacker does an exhaustive search of ONLY passwords

Well, yes. But consider the opposite case: the company doesn't prohibit these kinds of passwords, and the attacker does an exhaustive search of ONLY passwords that have sequential characters. That attack may be better even though they are only searching through a fraction of the total password space, since users will very often choose passwords that have sequential letters.