I'm actually in agreement with B-cell that Rockstar are not great at good mission design. Way too often their missions are too restrictive and railroaded and it clashes greatly with the otherwise open world. Thought you could flank out 10m and sneak up on the guard? Nope, that's out of bounds. Throw a knife at him? Nope, you need to approach him directly from the front. Headshot him before he can reach the alarm? Nope, that alarm is scripted. Having more freedom of approach in most missions wouldn't really hurt the game.
All that being said, it is easy to forgive when you can spend hundreds of hours just taking in the open world and still finding new cool details or stuff to do.
I'd agree that the missions clash with the free-roam stuff to a degree, I disagree with the video he linked and the claim that it's bad game design. You are just given too much of a false sense of freedom in the open world that you do not have in the missions.
But to be honest, there isn't a lot of freedom in how you complete missions in most games. Usually you can sneak or guns blasting and that's it. Otherwise the missions are almost always tightly designed objectives.
Even if you look at something like BotW, you can get things done in a lot of ways, but the core goal is strictly a limiting thing. You HAVE to kill the boss, how you kill him is sort of up to you, but the goal is the same. Go anywhere doesn't always mean freedom, because while you can go anywhere in Zelda you cannot do anything you want. The korak seeds require specific things to achieve, the enemies can only be beaten through combat of some sort, etc etc.
So everything has a limiting factor. And usually when there are even just two or three options with how to tackle a given task in a game, things start to get messy. The AI bugs, the mission itself bugs, things don't always go according to the game's script and when that happens shit breaks. So Rockstar trying to keep the actual game part of their games tight and working properly is not outdated, or bad. It's done to preserve the quality of what's on offer.
You see when you are committing chaos in the over-world, blowing shit up, getting 5-star wanted levels, the mayhem is all well and good. And during these situations when the AI breaks, the player usually finds it hilarious. However if the AI breaks during a critical mission the player is focused on completing, they tend to be far less forgiving. This is why Rockstar does things they way they do. And considering GTA V has made more money than any other movie, video game, TV show, in history.....I think it works out just fine.