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.
In that particular situation, perhaps it's not better to use the driver. Perhaps you are the exception with your current game.
That said, I think you likely have something pretty wrong with your swing for that to be true. The driver is the most forgiving and easiest to hit club in the bag. You also might have a driver that is just not fit for you at all. Could be many things. I would personally tell you to work on fixing your driver, because if you can get that club out 250+ nearly every time, that's huge. Most golfers can't do that.
I would also hazard a guess that your 3 wood is wilder than you think. I really find it hard to believe that you'd have a much wider dispersion with a driver than a 3 wood.
A thread that might be helpful to you:
On your last question, I think pros hit 3 woods way too often. It really only makes sense to do if you're trying to avoid trouble and you can do that by laying back.
Your goal should be to get as close as possible to the green on a par 5 without risking too much trouble. I'm guessing at your level laying up with a long iron isn't ideal because you're going to have a huge dispersion with those clubs. It would depend on the hole, because if you can get it closer to green with one of those clubs without risking a penalty stroke, it could still make sense.
The real point I was making is about the partial wedge idea. You will take fewer strokes the closer you are to the hole, full stop. So if the choice is to lay up with an 8 iron to get a full sand wedge or lay up with a 6 iron to get a half sand wedge, you should always go for the 6 iron. I see good players playing up to a full wedge distance all the time, and it's the wrong decision (absent potential penalty strokes). If you can't get to the green, get as close as possible.
This is stuff that's explained in LSW and Every Stroke Counts, if you are interested in reading more about it. I'd highly recommend LSW.
List your favorite tournaments to watch on TV.
Here are mine, in order:
1. The Open Championship
2. The Masters
3. The United States Open Championship
4. The PGA Championship
Jack Nicklaus and Tiger Woods covet majors more than any other events. That has the 2 best players, spanning over 50 years, coveting the majors. As Jack and Tiger go, so goes golf.
My take was the difference between 'still' and 'steady' - semantics, I know, but I take still to mean 'kept at the same position as at address', rather than rotating freely through. Either way, we're getting at the same point. I think.