In the case of that one example, you're dealing w/ two different bands (2.4GHz and 5GHz), each of which supports 450Mbps. Each one of those bands is actually three channels within the band, each capable of 150Mbps (that's why these wireless N routers are always sold in 150Mbps steps; 150Mbps, 300Mbps, 450Mbps, etc.). The chipsets aren’t any faster/better, they just keep bonding more channels together. And why you see so many antennas, one for each channel.
So if you work it all out, MIMO has the potential for 6 concurrent streams of 150Mbps, 3 of them on 2.4Ghz, the other 3 on 5Ghz.
However, that assumes your wireless client adapters are compatible w/ those freqs *and* support MIMO! Not all do, in fact, probably most low-priced ones don't, or might even prove to be incompatible w/ some wireless routers. So if your smart TV, for example, has built-in wireless adapters, you may very well need to replace them.
That's why even though you can theoretically make it all work, at least on paper, it's still tricky, and perhaps expensive. And as you said, stated speeds are based on ideal conditions. Who knows what any one of us will experience in the real world.
So it's never easy and never a guarantee. Minimally you need to have a plan and understand how it could be done. But once executed, you just have to keep your fingers crossed and hope for the best.
That's why nothing beats a wired connection. I would strongly urge you to consider something like Gigabit powerline adapters or even MoCA (ethernet over coax), perhaps both. MoCA in particular can deliver 100Mbps or better in many cases. And while that's still shared across the MoCA link, it will probably prove more reliable, cheaper, and just plain more likely to work. Maybe 5-6 streams might be too much for it, but I bet 3-4 streams would work reasonably well.