These are myths that I hear a lot. Some are just eye rolling trivia but some can hurt.
1. Tour pros continuously vary their shot shape based on hole demand. Not true. They have one predominant shot shape they play almost all the time. Only when in jail or extreme condition do they actually try anything out of their comfort zone - which is smaller than most folks think.
2. Tour pros are like swing doctors. They know everything there is to know about the golf swing. Nope - they are simply phenomenal listeners and executors.
3. You must understand the swing in it's entirety to learn and become better - Yeah, good luck on that path.
4. To have lag just hold the angle of the shaft to forearm until impact. - Lag is a result of good mechanics and club position and path. Can't force it.
5. You must have a superlight grip pressure (2-3 on a scale of 1 to 10) to hit good shots. - While white knuckling is just bad, you do need more grip pressure than you think.
The problem is the twitter length version, get it as close to the hole as possible, is easy to read as, hit the longest club. Really the argument in LSW (backed by stats), is around a multi-faceted risk assessment. Simplifying less than the twitter version, hit it as far as possible without bringing "too much" risk into play. The long version is basically a law of total probability argument, where you assess the probability of various outcomes with each current shot choice, and weight them by the average shots to hole out given each outcome, and choose the lowest.
For example, you're sitting at 250 on a par 5. You go through the potential outcomes of an 8i and 3i and estimate average shots to hole out from each: on target, slightly off target, chunk, blade, in jail, in hazard, open look but super penal rough, OB, whatever. Then you think about the chances of these outcomes, and calculate the total expected score from each choice.
The point in LSW is that you can't go through a bunch of equations for every shot, but if you're accurate about your average shot dispersions across clubs, then the typical bogey or better golfer is often overestimating the increase in risk from going for the longer shot, and underestimating the decrease in expected number of shots to hole out from getting it closer.
The rule of thumb is that if there's not something in the layout that is a big risk at the longer distance but not at the short one – so in your case lateral hazard or big fairway thinning or big fairway bunker or much or penal rough or the like that starts at 75 yards out – then generally your lower expected total score is from hitting the longer club. The strokes you lose when you do hit an errant long iron but wouldn't have hit an errant short iron are more than made up for by the strokes you gain from having an approach half as long when you don't hit an errant shot.
Of course, it's always case by case and player by player.
If this is true, then club fitting would be purely entertainment also and make no difference. We could all use different clubs every time we played with no measurable effect on our score. I'm not so sure all the time, money and effort that has gone towards studying the benefits of club fitting and developing custom club programs and fitting carts and training techs how to conduct a club fitting session would have been spent if it's all just "entertainment".
Now, will there be a huge difference between the e6 and e7 for the average player? No. They are both 3 piece distance balls with the same type of cover, so the differences are not huge. Noticeable, but not huge. The difference between an e6 and a Pro V1 though will be dramatic. And the number of players that played the Pro V that have been recommended the e6 are in the tens of thousands. Not only is there a difference in the performance of those balls, but when you factor in the tendencies of the player the results can be substantial. If a 10-15 yard gain won't have any affect on the average player's score, then you wouldn't mind if you had to give up 10-15 yards of distance off your drives and 5-7 off your irons, correct? How would it affect your score if you had to tee off 25 yds further back on every hole? I'm guessing it would cost at least a couple of shots.
Can @iacas shoot 75 with his wife's clubs? Probably. That doesn't mean that the equipment doesn't matter. He would certainly need to make adjustments in his swing to hit them, which is hard to repeat precisely, so it would limit him from playing his best.