Wow not many ppl are giving helpful responses...
Anyway, I would say don't feel bad about getting a new camera, as much as people say its not about the gear shooting something like wildlife where story/ controlled lighting play little to no role for most amateurs, getting new gear is a great way to get a better image. Depending on your budget the sony a7ii might be a great alternative (5-axis stab) if the a7s is too expensive, I've seen some low light footage online and it does remarkably well. And yes there will always be a better camera in the future but eventually you will have to take the plunge so why not now?
what is your budget btw? sorry if you already said it
This may come from a place of complete ignorance and missing points completely but after seeing these types of videos I am always left somewhat bothered. I can't help but feel that these videos lack an objective perspective and that because a director is considered either a legend(in this case Kurosawa) or a bonehead like Micheal Bay, that all their respective shots are described in that positive/negative light. For example the description at 2:30 "one of my favorite things is that his blocking is unrealistic and exaggerated", if this was a video essay on Micheal Bay that point would have been the same but that exact opposite tone,"too often does Micheal Bay rely on over the top, unrealistic and exaggerated blocking, he lacks subtlety and treats the audience like children". Anyway I hope I don't come across as disrespectful because I still appreciate Tony Zhou's videos but I am weary of directors or artists in general of being placed in these boxes of unequivocal good or bad based on public opinion.