Buffered mults are more like "insurance" these days. They exist because, in past designs, there could be a certain amount of "voltage sag". Much of this was due to bad exponential converter design and/or lower-quality components, but these days many designers have front ends on their fixed CV conversion that minimizes this issue. But notice I said "minimizes"...it doesn't 100% fix it, as you can pile enough destinations for CVs onto the same CV bus that the destination modules will mistrack just like the "bad old days".
Rule of thumb: if you're splitting a CV with a mult that then goes to more than four other modules, you're probably better off using a buffered mult. Even if all of the modules on that bus have really good CV sag figures, if you stack enough of them on that one CV, you'll still be subject to sag eventually.
As for the VCAs...OK, sure, that one user in their YT video doesn't really have them in evidence. And while that approach might work for THEM, it's probably not a good idea. It sounds fine in this example, but let's say you wanted to do something that required both VCA control over audio levels AND over modulation levels. Now you have a problem. It might be nice for some synthesists to have a dedicated cab for a specific sound production method, but the vast majority of us don't have that luxury, and so we recognize that you have to have bread-and-butter modules such as VCAs for the times you might want them. And they are QUITE necessary...boring, yes, but essential. Building a rig without VCAs because they're "boring" and nowhere as snazzy as all those other modules with the blinkylights is sort of akin to building a car without a radiator. Radiators are boring, they just dissipate heat...but just try driving a car that doesn't have one but which does have a water cooled engine. You won't be going very far.
And a word about YouTube as a method of learning modular synthesis...
It needs to be said that there are a few synthesists on YT who absolutely know what they're doing. 100%. But like any other source of information on the Internet, there's also a lot of utter BS and nonsense out there, plus a lot of stuff that's sort of misleading. And this is a case of the latter; clearly, whoever is in the clip is experienced...and what they're using works for their purposes. But this DOES NOT mean that a copy of their rig will be something usable in the hands of someone beginning with modular synths. They have an approach that works, but it's not one that will result in a modular rig that's usable across a wide range of uses.
So, unless you like blowing through a lot of money and experiencing plenty of frustration, it's essential to be very careful about what sources of info are ones that'll work for your specific situation. A much better approach would be to look at a number of builds by a lot of different synthesists and see what elements you encounter that work for you and those which are dead-ends. And one of the biggest dead-ends is to copy a user's bespoke device, built for their techniques and methods alone. Those builds might make for showy YT clips, but they don't help beginning modular users.