I do not know the exact numbers, but up until maybe five years ago Disney would sell like 200 single park tickets for DCA a day, and thousands (maybe tens of thousands) for DL each day. Nobody (well 200 people a day) wanted to go only to DCA.
Going way back til at least 2003 - my first visit to DCA - Disney made all multi-day tickets automatic park hoppers. Originally (in 2001) they tried to charge a premium for hopping and nobody (well, very few) paid and DCA attendance was way down. In order to get bodies inside DCA they offered "free" hopping. In other words, if you bought a two+ day ticket to DL you could go to DCA "for free". They just quietly changed this maybe a year ago and now you have to pay extra for hoppers.
With all of the work at DCA and especially with WOC and LMAUA - and now with CL and BVS - folks are coming to DCA on its own merits. But historically not many did.
During our first visit in 2003 I loved, loved, loved Soarin but not much else at DCA. Screamin was cool but lacked theming (and still does BTW). They had trailers going up and down the parade route with blaring rock bands and some kind of X-Games competition happening by Paradise Pier.

It felt more like Six Flags to me than Disney.
Later they added ToT (2004), TTwC (2005) and DCA started to feel much more Disney to me. With the work over the last five years they have nailed it. I have not of course seen BVS yet but I saw the preview at
D23 Expo and heard the imagineers talk about it at the BVS session, and I already know they have a hit on their hands. DCA will emerge as a legitimate standalone park on June 15. Can you imagine what it will be like this summer when DCA will be drawing folks
away from DL?!?!?