Keeping up with the topic of simplicity, how do you measure progress for a given lift? More reps with the same weight, more sets in the same time interval, heavier weight, for the same or higher sets or reps, same reps/sets in shorter time interval. Improvement in one of these parameters leads to the improvement in another. There are several numerous basic principles of how to do it, none are a rocket science. Set the goal and progress accordingly.
A "professionally designed program" would be me hiring a coach who will guide me and adjust my training to my level of training, age, injury history, will tweak it to fit my ability to recover and fit it in with a sport I may be doing. That's where complexity comes in. For a stand alone GPP program though simple progression goals will do just fine. Until you hit a certain performance level, then complexity becomes unavoidable. But then again, if the goal is not a sport where you can be the first, the usefulness of GPP has limits.
I get it why many people want to take the thought out of the equation. Get to gym, hit the numbers, go home. There is also this idea that someone knows more than you and you should listen to them. I personally got burned more often than not when I believed that. But even that is not relevant. For me the process itself is part of the goal. It's like hunting: you can get a guide who will take you to where deer are, you shoot one, get the trophy and be proud of yourself. Easier yet, go to the local shop and get as much venison as you want. Or you can spend a few days looking for one and maybe not getting a kill for several trips. But the reward to do it all by yourself is way more than just eating a steak on a weekend. Now you know you are a predator.
As several posters already said, to each his own. I would just say, don't shortchange yourself, designing a training program is not hard if you give it a bit of a thought. Again, just my opinion.