This is the difference between good instruction now and lessons from pros 25 years ago. Back then, they were not really paying too much attention to stroke fundamentals- mostly the pro instruction was which ball to hit next and where to try and land after that shot. The level of attention paid to alignment, eye movements, straight strokes, etc. was minimal from older pros during paid lessons.
Without all the proper fundamentals, including a straight stroke, anyone is doomed to mediocrity.   My two favorite teaching aids for pool are Mark Wilson's " Play Great Pool" - read it and stay with it for a full year including constant video review of your fundamentals until you have an excellent foundation for the game.
Couple doing that with some serious competition and keep the book " emotional Intelligence"  in your back pocket- because most of the folks who get the fundamentals right, but break down along the way in competition, are probably letting poor emotional management in competitive situations dominate their ability to perform the way they had trained so hard to accomplish in battle.
You fight the fight on two fronts - one is to have as flawless as possible - your pool stroking foundation; and two, is to have the mental capacity to allow yourself to perform consistently at or close to maximum ability. Most of the very best have both things going for them way more than the average competitor.