What do we mean by spend? The annual cost of Barca squad is twice as Atletico, we were top 4 in Europe last year.
Atletico is distant 3rd in La Liga financial ability, and they perform the same way.
Transfer budget is a fraction of money clubs spend, and even if you consider it as the money Atletico has ignored their squad reinforcement after 2019 and it was mostly old farts that Simeone managed to overachieve with them, last summer was the first one they actually broke the bank to really improve it, but even then their squad was still not half good as Barca or Madrid.
Atletico might have stalled, but that is an actual achievement, they should have declined far more by now. Unless a top coach is available, their board knows they are most likely downgrading if they change coach.