I am aware of that, what I am saying, IMO, it is not a good strategy. I have had that situation come at me more than once in my old security days. And I can tell you for a fact, if I tried to kick the oncoming train, it would not have ended so well. Especially with the WWF (now WWE) wrestler solid muscle and over 200lbs) who was hopped up on something who came charging at me..... sidestep, trip, he face planted on the pavement.... problem solved. And I don't care how rooted you think you are in that, I seriously doubt it would have stopped him and only hurt you.
It takes time to develop any "door guarding" skill. It's up to how much time that you are willing to develop a certain skill. You may be able to stop a 200 lb guy with 5 years kicking training. But to stop a 300 lb guy may take more years than that.
IMO, a good kick can be your 1st line defense. It's a good "door guarding" skill to train. The moment that someone throws a punch at you, the moment that your leg kicks out without thinking. That's what we all want to achieve.
I think there's two issues here.
1: You are talking about two different situations. When someone is "bullrushing" you, particularly someone who seems very strong, throwing a kick and trying to root/absorb the impact is not going to work very well, and in that situation a redirect works better. When someone is coming towards you, but not rushing/overcommitting, redirecting is a bit tougher to pull off, so throwing out a kick to catch them works better.
2: There's a second part to that drill/kick that wang is talking about, which I don't see a lot of people train/even know of. When they are larger you
don't want to root it into the ground, specifically for the concerns Xue has. However, if you pick up your rear leg (assuming you're kicking with the lead) right before impact, they still take a large brunt of the force. You don't want to jump with it though, since then the weight is going nowhere and you're just pushed buck/thrown off balance. Essentially it's a backstep that you take at that exact moment, shifting your feet back, and looks almost like an awkward one-legged skip. Doing it this way alleviates the force so you're not rushed over, while also still giving them a large portion of the damage. And from experience on both ends of it, the harder they're rushing at you, the more it hurts.
It's very tough to pull off; took me close to 6 months before I got it correct once, but once you understand it and the timing it can work consistently and well. The issue is people don't teach that portion, and get content trying to overpower the attacker/stand their ground instead.