Funniest thing is what has made the single biggest change in me mentally has been a simple stop shot drill
Not surprising. Not sure how it's helped you mentally but it should definitely help your position play. The stop shot is the basis for all position play. If one can't stop the CB from all distances and at varying speeds they'll constantly struggle with position. Saw you've only been playing 4 yrs. and looks like you've made good progress. If you want to continue improving, particularly in 14.1, there's a few areas you might want to focus on.
The aforementioned position play is one, especially with regards to finesse around the rack area. Soft draw, sliding the CB sideways a couple inches, hitting a cluster in an exact spot are key to manipulating the balls into advantageous positions.
Shot selection and angle selection is another area that will make a big difference in your game. You have way too much CB movement and traveling across position zones and it's making things much harder than they need to be and often leaving you with harder +/or subpar breakshots. (your run stopped by missing the 4 ball but I'd submit that the less than ideal breakshot on the 15 was a contributing factor by not leaving you a whole lot to work with)
Even still, you had a few options but they required obtaining very precise angles. If the 11 passed the 8 the best would have been getting straight on the 4 and breaking them with the 11. (perhaps that was your plan?) If not you had 3 other options.
1) When shooting the 1, tried to get straight on the 12 in the upper corner, stop, and play the 9 coming off the foot rail up into the balls with speed. (no insurance so as much speed as possible without missing the ball is essential.
2) From where you were on the 9 it looked like you could have drawn up into the rack. If you could miss the 11 and go into the 6 it would have loosened up a few balls and the 4 +/or the 11 or the striped ball next to the 7 in the opposite side would have offered a decent amount of insurance. Speed would be very important here for generating the correct angle from the 9 to the 6.
3) When shooting the 1 get straight on the 9. Stop and play the 11 in the upper left corner with good follow. Loosens a few balls and the 4 is excellent insurance.
These were all viable options. I would have chosen #1 because even if I didn't get straight on the 12 options 2+3 would have still been there.
I watched a few of your videos and saw a recurring theme most of the time.
Poor shot and angle selection is holding you back. It's forcing you to shoot harder shots, play across position zones and be left with no insurance balls much of the time, all of which are run killers. Correcting these things will make a big difference.
How to do it? It starts with the thought process when evaluating the table. Setting goals and having a clear purpose for every ball you shoot is essential. Much of this simply requires more time and experience but then again I've seen hundreds of guys at about your level that never improved from there.
One thing you might do is study your own videos and see how you might have done something different with regards to what I mentioned above about insurance balls, etc. The one where you run 14, miss then run 36 offers a good example of the thought process required in straight pool. I'm starting at the beginning of the 36 ball run. Most would agree that it's a fairly easy rack but there are a few problems and the initial evaluation should be geared towards addressing them quickly and in a natural, efficient manner.
I paused the video as you were about to shoot the 11 ball after the break shot. I don't know what you did after that. I'll just give you my thoughts on what I think should be done in this situation.
The break shot for the next rack is not in the equation at this point. The problem areas are the 5,7,13 +15. With the exception of the 6 those balls have no pocket or only one pocket. I need to change that right away and do it in a way that allows me to shoot easy shots with natural position which carry a very high degree of success.
I'm going to shoot the 11,1 + 6. From the 6 I'd like to position the CB between the 5 + 13 with my goal being to get fairly straight in on both balls + eliminate them next. If position allows it I'd like to go 13 then 5. Reason being is because a stop shot on the 5 puts me in perfect line on the 12 so I can go and get rid of the 15 and possibly the 7 also.
At this point all problems are gone and I'm left with all the balls in the middle of the table with multiple break shots and unlimited options. This was a pretty easy rack and many people would have done it differently but the goal should be the same. Eliminate problems quickly and efficiently while maintaining insurance in case of making slight position errors along the way.
Many racks will be much harder but the thought process should remain the same regardless. If doing so means shooting a harder shot or more intricate position then IMO that's the way to go. Choosing to shoot a hard shot earlier instead of waiting until you're forced into it is usually the best option.
As far as intricate precise position goes, the brainwash drill is excellent in that regard.
Hope this helps a little.