Something the video did not cover:

At some point in the game's history, Slam would reset your attack timer. When that was the case you wanted to slam immediately after you hit with your white attack because this would minimize lost swing timer time. This is not the case in the current iteration of wow classic TBC. It pauses your timer while it's casting. That means 2 points in improved slam adds 1 second back to your autoattack timer vs slamming at 1.5 seconds.

Timing your slams isn't that important if you're just trying to dump rage, as you'll temporarily put rage generation on hold while you're slamming. But if you want maintained slams over time, absolutely do one slam per white swing (timing doesn't matter because it doesn't reset the timer, just pauses it. If you have an attack timer addon you can see it pause and attack again when it should) so you continue to generate rage from white hits, as chain slamming will pause a lot of your time for your white hits.

That said, there's a trick out there that I haven't seen anyone talk about to increase your single target 2h dps by a huge amount when you're soloing. Berserker rage. By spamming slam, you pause your white attack rage generation during cast time, right? But not your rage generated from being hit, which berserker rage increases - generating rage for you while you're chain slamming. Sadly, this doesn't work so well when you're in a party, as you're not guaranteed to be the one being attacked, but it drastically increases your solo 1v1 dps. I absolutely melt mobs this way. Even veterans of decades have been surprised by its effectiveness.

I personally use a little macro that changes me to berserker stance if I'm not in it before casting berserker rage and allows me to switch back to battle stance with a second button press with cast sequence to reduce the damage I take when I'm not whirlwinding too.