I've read fairly extensively on the subject and my personal opinion, which might not match those of others, is that the FBI agents who confronted the suspects were outgunned. More than that, their training did not prepare them to go up against former military trained adversaries whose first instinct was to shoot their way out of the situation. Police/law enforcement mentality/tactics vs military mentality/tactics.
Several agents also had setbacks right from the start (losing glasses, losing firearms, firearms becoming inoperable.) They were somewhat effective in hitting the suspects but not in stopping them DRT. Revolvers against a Mini 14 and a shotgun proved to be a lopsided encounter. Had they been able to wait for some of the other agents who were more effectively armed, things would have possibly ended very differently.
I've never been in law enforcement, only in the military, so I'm speculating, but it seems to me the current prevalence of the SWAT type training and mentality is what resulted from this and similar encounters, Uvalde withstanding.