This may be off slightly from the original text of your post but I think serves to give an example of how good/proper isolation can work.
I have (2) Martin Logan Depth i subs in my small listening space. I’ve been using the stock (pretty darn good quality) supplied spikes for years. I have a few sets of Stillpoints Ultra SS that are unused and had always planned on using some under the MLs. I just needed to order some adapters and a few Bullet Spikes and the installation was very easy. I was as you say, "shocked"..... at how much more, clear lower bass info there is now that I really never heard before. The MLs have 3 equally opposing 8" drivers that cancel out almost all vibrations ( the main reason I like them so much in my situation). Having said that and even though they are on a suspended floor, I get this great upgrade in SQ. Oh yeah, the center stage, especially vocals have an enticing new clarity that draws you in.