beatmatching wasnt a thing, since lining up the grids is all you needed to do
Well, depending slightly on your genres, but beatgrids are correct about 80-85% of the time in EDM-ish music, far less in more traditional hand-drummed stuff clearly. And depending on your DJ software multiple BPM tracks can throw of a good grid.
Leaving you with still 1 in 5 to 10 tracks to mix manually, even on an SX. Also, being the DJ, you are in charge of the sync button. Don’t touch it and ALL your mixes will have to be manual. No need for another controller I would think.
I have been using the SX with (mainly) Mixvibes Cross for the last almost 2 years now and have not had a sound drop in all that time, so your trouble are not “typical” of the SX, but must have had to do with your particular SX (hardware failure) or the combination of SX, software and laptop (including drivers, USB ports/hubs/etx.)
I am assuming you are talking XDJ-RX, not the DDJ-RX (RekordBox), which still offers the same sync features if your tracks are RB prepared. The sync/master buttons being a bit of a clue there LOL.
Good you have found something that works (better) for you, I was just surprised by the argumentation (clearly the sound drops were serious enough to have a look at, regardless of what controller would have caused those).