No they are not spending more than they are earning, but most of them are just surviving doing one of the most dangerous combat sport on earth.
I watched some interviews and fighters spoke how much they pay for fight camps, and it's lot more money than you think.
Higher ranked fighters does earn much more if they are unbeatable like Khabib or if they trashtalk like McGregor did in his prime.
If we look at the statistics boxing is probably considered more dangerous due to the long term effects that getting punched in the head does, compared to hard blows, but non repeated punches. Obviously, the research is still being conducted (including other sports like football), but I expect that Boxing does have more long term effects, especially considering the effect that the boxing glove has, i.e padding the blows allowing more blows than a smaller glove like the UFC does.
Since, if you get hurt in UFC its likely game over, and if its not your trying to dive to the legs, and survive. Boxing, quite often the blow isn't enough to knock you over, but your dazed enough to not know exactly what's going on, and therefore take more shots.
All these talks about UFC salaries started after YouTubers started to beat UFC fighters and boast with high payment and easy money. Jake Paul vs Ben Askren, Tyron Woodley - Jake trolled Dana White with huge cheques and numbers of PPV sold. Jake Paul was planned to fight Tommy Fury, but after Tommy got injured, he has fought Woodley for the second. Long story short, only 65k PPV were sold
I think that every UFC event gets +100k PPV sold. Found that UFC 268 sold 700k PPV. I think UFC 269 (Poirier vs Oliveira) sold even more, and Ngannou vs Gane is definitely gonna set a record.
It annoys me as a fan, I can't imagine how annoyed MMA fighters are to see that people like Jake Paul who are completely new to the sport are making more money in one fight than most UFC fighters will ever hold in their careers. Its quite sickening, I'm not sure if that's Dana's fault though or if its just the ridiculous amount of money that Boxing has come to spend.