Hey man, there is nothing wrong with a tight grip and there are ways to make it work....starting out loose and in a different part of the hand than where you finish just isn't one of them. If you are going to play around with grips (something I suggest everyone do early on and then just to play around as an exercise once in a blue moon even when experienced) check out my TLDR post in the Thumb Straight Down thread either here in instructors or main forum. There I go into different grips and why they work (stabilizers used). Play around. Hopefully one clicks for you. But FWIW, Bob's advice on contact around the cue throughout is a solid starting point for many successful grips, esp those that close tight bc the cue is already in contact with the hand and the other fingers meet it there rather than the fingers lifting the cue into that position like you were doing in the vid.
Good Luck
I think the next step for me is to see if I'm tightening up on other "power" shots, break, and follow
not saying there's anything wrong with a tight grip, but aesthetically I just don't like it for myself
let the games continue...