OK, I'm still seeing domination
, tho Ziggy is a little
more dominant than your other 2 videos.. Face it, Ziggy is a bully cat (red tabbies often are) and is definitely getting his jollies out of harassing Zuzu. Yes she's pissed (& hissed!) off at him and mighty annoyed with her ears flattened and yowling, and really wants nothing to do with him going from one hiding place to another.
So the ?, let them continue or break them up? The problem is, yes he's still kittenish, but he may escalate this stalk and pounce to more seious cat fights. I would break it up, as it doesn't take much to break the skin with claws or teeth, and cats can easily get an infection
that often isn't detected right away, then it's a trip to the vet for antibiotics...$$$$!!
Besides, it bothers you
. I'm the same way and I don't tolerate too rough playing. My two have "play fights" but with claws in and they've never escalated into a serious cat fight. One day one dominates and chases, another time it's the other. I can easily distract them with my voice or redirect with a toy. If this doesn't work for you, give yourself some peace and do the room-juggle routine, or rehome one of them.
As for catnip...no it will not make him any more aggressive---he is already naturally. I doubt it has anything to do with his early upbringing. I think your vet will tell you what you've already heard here. Catnip actually has the opposite effect. There is initial excitement followed by relaxation. You can give him some catnip to eat.