I joined to work on meta ads semi-recently. My thinking was that they were under invested in techniques I knew were successful from my time at Google.
What I found was a lot of smart people who knew they were under invested and we're capable of closing the gap, but the infrastructure they sat upon was too hard to use to do anything different, and management that rewarded the appearance of great work more than great work. The result was a lot of config changes making noise in metrics that could be read positively, without implementing the state of the art systems that took a year before you could write a fancy success workplace post about it. That would risk poor performance reviews and the shuffling of reasources away from your team as a result.
And now, it's becoming apparent that the very very smart people started leaving after the stock dropped and the replacements are both more expensive and less able to get used to Facebook's infra. The result on the ground looks like a very serious engineering death spiral that management has not signaled they understand or have a grip on.