In a way, they do. Simply do enough damage to kill a creature in one-shot. In reference to PWK, it again seems powerful on the surface level but in practicality it's "do 100 damage. If that doesn't kill, undo the damage." And it's attached to magic with all it's drawbacks.
Not to mention, the monk has an ability extremely similar to this in their Open Hand tradition.
If you use the DMG object rules and assume that the portcullis is the most resilient option (large, resilient), the fighter can tear through it before a round is over.
It's explicitly possible to bend portcullis bars in the DMG, so if the DM calls for a strength check, the fighter can "take20" and get as high as a DC 28. Not only without magic assistance, but with a straight strength check with no skills/tools.
Or, if they simply want to lift it, then as long as the weight of the portcullis is less than 600lbs, the fighter can lift it easily with no ability check. If they can't, the DM can call for a strength check where they, again, get a huge possible score.
Any character can do this with the Pirate background. And while you may think it relies on DM fiat, there really isn't a way to give a feature like that to a character without it being frustrating for the DM. I mean, even spells can't force an entire regiment to back down at a time. You can frighten or charm them or try to Mass Suggestion them, but there's still limits like saving throws and a finite number of creatures that can be magically suggested. A GOOlock would need very specific circumstances to attempt to imitate that.
Simply dealing damage isn't very interesting, nor does it do much to evoke the archetype of the legendary warrior. It's effectively the same thing you were doing at level 1. I never said it was powerful. Like
@Neonchameleon , I don't think the fighter needs help in that department.
Where I think the fighter needs help is "wow factor" and utility.
A PWK ability that is usable one per day isn't much in terms of combat power (the fighter could output that same damage in a relatively short window anyway). It's the "wow factor" of not having to do so.
The monk also being able to do so says to me that there's no big harm in letting the fighter do so. We're not disrupting a core niche here. If anything, we're giving the ability to the guy whose niche it belongs to.
Maybe the fighter could destroy the porticulis using the rules. Really depends on how strong the DM rules the porticulis and how well the fighter rolls. Also, I was envisioning more of a single attack type of thing, so that the fighter doesn't have to sacrifice all of his attacks for what amounts to going through the door.
Regarding taking 20, that doesn't exist in 5e.
Regarding lifting things that are within your encumbrance limit, I will refer you to earlier in the thread where we had a discussion about why people think characters should have to roll for lifting things that are within your allowance. And yes, there are folks who believe this is perfectly reasonable.
So, again, DM fiat, which is not ubiquitous from table to table. I can take the same fighter to the same adventure at three different tables and get three different results. One might let me lift the porticulis automatically. One might make me roll for it. One might decide that it weighs a ton and not permit me to even make the attempt. Spells work without fiat. Why can't the fighter have features that work without fiat?
Moreover, all of these are things that anyone with high strength can do. I'm talking about an exclusive fighter feature that would let the fighter do this exceptionally well. Better than others. Both for "wow factor" and utility.
Regarding your pirate intimidation, please refer to the above. My response would basically be a copy/paste with a few words changed for the context.