A lot of things I think of as "systems" are more baselines. For example, in the picture, where the ball is on the first rail, if I hit the ball 1/4 ball with a little english, that's where it's going to go. And of course, I know the running lines/tracks that connect rails 2-3-4-5. Half ball hit and they all shift one diamond. If you want to do that all by feel, knock yourself out. I find it's a massive shortcut to just know these incredibly easy to memorize numbers. I just look at where the first ball is and I know, "It's going to 30, will hit the 1st diamond from the corner on the 3rd rail, the first diamond on the 4th long rail and then heads back towards the other corner. Takes me literally two seconds in my head.
Then I know where the second rail will hit/needs to be hit based on where the first rail is hit. Again, easy to memorize. If there's a position where it's easier to base it off of the second rail hit, you know that already. And then again you know the track that goes to rail 3-4-5. That covers probably 50+% of the shots you're going to make. It's like a simple system that connects all kinds of shots together.
Simple stuff like if you're doing a short table shot, you hit the first ball with lots of spin and go perpendicular into the long rail, the spread will be 18. So if the first ball is at 10, the third rail will be hit at 8. Works the same way going the long table, except it's double, 36. That kind of thing takes me ten seconds to memorize. Personally I wouldn't bother feeling it out.
Same thing, like if the object ball is touching the long rail and you hit it 1/2 ball with no english, do you know exactly what the cueball diamond spread is? I just memorize that and then I can adjust from there. I don't see why I would want to "feel" that when I can just shoot the shot once and memorize one number. If you memorize 1/4 and 1/8, too, now you can make the cueball go practically anywhere you want.
Now say a rail first umbrella type shot, yeah I'll just go system on that. If I had five years to practice them all day long, I would but I don't.
Not all "systems" are 50-40-(2/30) or whatever.