IDA has been mainstream among reverse engineers for at least 15 years, and equivalents such as win32dasm existed before that, so there is not really a notion of a post-IDA world.
Closed source is very much a huge barrier in verifying what software is doing, just as much as it always has been. I say that as someone who has been reversing engineering professionally for much of that time.
The number of people with the expertise and access to IDA is a tiny subset of those who can just skim source code. And those who are competent reverse engineers take 10x-100x longer going that route. An even smaller subset of those have the inclination to even bother doing this for free in their spare time.
Closed source is very much a huge barrier in verifying what software is doing, just as much as it always has been. I say that as someone who has been reversing engineering professionally for much of that time.
The number of people with the expertise and access to IDA is a tiny subset of those who can just skim source code. And those who are competent reverse engineers take 10x-100x longer going that route. An even smaller subset of those have the inclination to even bother doing this for free in their spare time.