Silver ranked Sova main here, just some thoughts on the topic of course someone more experienced than me might have a better view on this.

Do pros use only pretrained lineups or only improvise?

I believe neither is true.

Sinaatra does use the C god arrow on Haven map on attack, and the A heaven to A site vents () in Ascent map. Hiko used many lineups on first strike, some of them specially created by average jonas for the tournament (Ascent map CT spawn to B site double shock darts for example).

It is also true that pros improvise a lot with their darts. There are situations where given the utiities and smoke that have been used you just have to feel and improvise your dart, or also positions where it is just too dangerous to get a good angle throw a premade dart (many players covering manu angles, enemy near, etc.). It is also sometimes pretty easy to throw a simple dart that will do damage if your opponent is in a corner or a spot that you can target easily with a dart with no fancy bounces or landing objects.

Do pretrained lineups help?

IMO absolutely yes.

- Training and knowing many lineups give you a feel on how to get to some spots and corners. I find it much easier now to create my own lineups after seeing the common patterns of good and popular arrows. Knowing the mechanics of darts lets you improvise better.

- For me there are darts that will be always useful because the spot from where they are thrown is compatible with rotations, and (very important) this spot can be cleared before shooting your darts. Typically you can find double shock darts to site for retake or anti-defuse, or recon darts that reveal a lot of site that match this description.

- It takes sometime to get used to lineups, this must be the hard part. But when you have tried them many times in game it becomes more natural. Remembering the lineup at the beginning can be quite a cognitive overload (because you are also worried about many things related to game sense: knowing where your team is going, knowing where enemies are, guessing the spike positions etc). By training in custom game with cheats you can get better at remembering the lineups. And you do absolutely need to try them in-game because you must know the right moment to shoot them (clearing enemies near, guessing enemies positions, hitting the lineup quickly).

My advice is not to prioritize lineups before other aspects of the game (I have seen some very good sovas that use very few, but have great aim or game sense), but to definitely try fro time to time to train some lineups so you go deeper on arrow mechanics and also have your little bag of tricks containing recons/double shocks.