I was told years ago that "You don't own it til you've worn it for a year". Now that's a bit of oversimplified bro science, but there's some truth to it.
It's this theory that has led me away from the traditional bulk then cut strategy.
Now this pertains to me and my experience and may or may not pertain to you. When we add muscle in a cycle, its far from permanent and it literally takes everything we've got to maintain it and stay in an anabolic state, especially after our cycle. Guys brag about how much of their gains they kept during or at the end of pct. But they rarely come back 2 or 3 months after pct and admit that continued to lose size or weight. Sometimes taking a break for 1 week is enough to lose the edge and the 1/2" gain that we worked so hard to achieve.
Taking into consideration how hard it is to gain actual, real, lean muscle - it seems illogical to immediately follow this achievement by moving toward a caloric deficit. In my mind, this would greatly increase the likelihood of losing some of the newly acquired (or rented) muscle.
So I tend to lean toward a constant focus of clean, lean mass gains and continually tweaking an adjusting things to prevent your body from adapting. I call it an anti-routine.
What you are saying is true to an extent. You are describing someone who bulks on cycle then immediately cuts after cycle in pct or soon after....which is a sure way to lose gains no doubt...but that is not what we are talking about here. We are talking about bulking and cutting in the same cycle which changes everything. While you are on s superphysiological level of exogenous hormones, your body will not lose any of the gains you made by going into a moderate cutting defecit while still on cycle. Hell, a lot of people still add muscle and plenty of gains while in a defecit on cycle.
On cycle cutting and off cycle cutting is apples to oranges