Yes, lofty is warm, which is why Santi wants you to wash it. Most people just prefer them a little packed down as they are still plenty warm but less bulky and floaty. It’s a trade off that’s worth it for some. People also avoid washing Thinsulate because you can screw it up if done wrong and it’s more of a PITA compared to fleece undergarments. I personally wash (which is rare anyway) because I’d rather be warm with a bit more lead on. That said, I avoid the Santi suit outside of winter dives as I’m more comfortable layering Forth Element fleece down to 40 deg.Floaty is warm, you want that. Dead air space is what keeps the heat in.
The problem with washing is that thinsulate is fairly loose material, almost like sheets of cotten wool. When it gets wet, it tends to get all clumpy. That's why you're not supposed to hang dry those suits. It's also the reason why the better/pricer suits are quilted.
That stuff you can wash but is not quite as warm but it will hold up better than thinsulate in my experience. Usually, when you wash stuff it loses some fibers every time.