Not descartes but used to have 4 OG LS50 plus a (now broken) sub in a small room. Long story short, got 4 R3 and an R2c but due to an impending move, only use two R3 with phantom center right now.
R3 without sub is a lot more capable than an LS50 but does not quite replace the sub, I think.
My opinion is that anyone saying a sub is not required hasnt heard their speakers with one or two well integrated subwoofers, or is in the "I dont like when movies get loud” camp or some other variation.
After integrating a Topping pre90 preamplifier it became extremely easy for me to test my R3 with and without subs because I get to turn off my subs with one click (output to XLR+RCA, XLR, RCA). When you release the speakers of their low end duties and allow two subwoofers to take over, the whole sound is absolutely different. Highs, mids and lows change dramatically, it doesnt really matter if the output level is low or high.
So, no, an R3, or mostly any other speaker that doesnt go as low as 20-30hz, doesnt substitute a subwoofer imho. Even those that go as low as 20hz can benefit greatly from a subwoofer because as I think I said in this same thread, the crucial variable that doesnt get too much attention is how distortion increases dramatically in most speakers from certain range. They market their products as being capable of reaching certain low frequency, but they dont mention that they get there with great distortion when compared to the levels achieved from say 100hz and up.