Possession is such an interesting thing in FM. I remember back in FM10 having over 70% possession one match against Arsenal, the most I'd ever had by far at that point, and lost 2-0 to two counterattacking goals scored by Bendtner. I remember winning the Champions League final against Inter, in that same save, 5-0 with 35% possession. Neither was by design as back then I knew slightly less than I do now and possession wasn't on my mind. Just scoring as many goals as possible. But somewhere along the way I got it in my head that top teams don't just win matches, dominate the ball so I set out to try to replicate that in game.
Initially I thought that playmakers were absolutely necessary for a possession based system. But tactic I created that gave me the highest possession numbers didn't have any whatsoever. I thought my team needed to have a more attacking mentality, with the idea that my players would be positioned higher up the pitch and pin my opposition in their half. It turned out my teams were better at keeping the ball on a more cautious mentality (probably because I like to use more attacking duties). I thought you needed to set your team up to play one and two touch football in order to get higher possession numbers. Over the years, I've had times where my teams have been better at keeping the ball when my players were given the freedom to and told to dribble.
As it's been said many times already, you can make the same type of system many ways, it just comes down to what you need to make it work with whatever players you have at your disposal. What helped me a lot when trying to figure out what worked with my team was watching portions of full matches. First time I did was a truly eye opening experience; being able to instantly see the impact a change to a duty or instruction has. From time to time I'll watch a bit on full match to diagnosis issues/when I'm testing things out.
I've made a few different systems over the years that satisfies that part of me that believed I needed to dominate both on the scoresheet and in possession numbers. I think the reason it always takes me so long to settle on something that I think checks off all the boxes for me is because, even when making something that focuses on possession, my top priority has and will always be goal scoring; there were and are simply things I will not compromise on because I feel they'll ultimately jeopardize my ability to put the ball in the back of the net. So I fully understand where Cleon is coming from on that matter in regards to FM.
In my experience with FM, there's a fine line between bossing possession while creating something in attack and unwittingly killing off the game by passing it around in the back and middle of the pitch. Like most things in FM, it's really comes down to balancing risk. Making a possession based system? There's the risk of blunting your attack in the name of ball retention. How much attacking risk are you willing to take on at the expense of possession? (Something I routinely do when my team has lots of the ball and are doing nothing with it, is take on more of that risk. I'll make changes that should deliberately reduce our possession) At the end of the day, even if I want the ball, I want to put it in the net and do so as much as possible (maybe we create chances with riskier passes or create opportunities to counter since I'm allowing my opposition more of the ball).
At the end of the day, dominating possession is fun, and it's aesthetically pleasing, but only when you're dominating the scoresheet as well.
Edit: It's really amazing how far FM has come. Maybe one day I'll finish my FM16 save and join the rest of you in the future