Fast deploy is good for many things, but that 5 times the testing effort means the few releases you do are higher quality. When it has to be perfect, like many embedded systems you don't do many releases.
If course the above assumes you actually do the 5 times the testing before release. Most companies skipped that, and it showed.
Automated tests are key for this. If you have those, it empowers deploying frequently. There is only so much that can break for a small delta. That typically also enables very targeted manual testing if you need that.
Many companies have the wrong reflex of releasing less often when things don't go smoothly so they can test more not realizing that if they release more often, they can get away with less testing because there is less new stuff that can break.
Automated tests are good, but even a large suite misses things. End to end full integration issues for example are very hard to automate and use a lot of time to run.
If course the above assumes you actually do the 5 times the testing before release. Most companies skipped that, and it showed.