Not sure how true this is:Yeah they don't cite a source so its hard to say. But even harder to say regarding Endgame, because it was made together with IW so finding an exact budget for it is hard. Either way, I highly doubt Endgame will be toppled by Joker.
Joker Set to Earn Almost as Much Profit as Avengers: Endgame
Using normal takings ratios, Endgame brought in approximately $1.2B for Disney while Joker will bring in roughly $500m (based on estimated overall $350m dom and $750m international). I expect Endgame will make much more from TV deals and home entertainment sales as well, but even assuming that's the same I really can't see Endgame costing $700m total, never mind $700m more than Joker.
I'm really not knowledgeable in this regard, but I'd say the estimates of $600m cost for Endgame are probably okay, meaning that's a $600m profit from the box office. Joker's BO profit will probably be more like $350-400m, so its way off. Could well be touch and go with Infinity War though, which is in second place for comic book movies, ($900m BO taking and a ~$500m budget put it at $400m profit). I'd back IW making more from TV and home as well though, so maybe IW will still hold onto second place. Not really any way to tell for sure.
Anyway, all 3 of these movies made ridiculous profit, and are seriously impressive in many different ways.