I'm a 3.5 and 4.0 usta singles player. I love to geek out on racquets and tennis physics.
I occasionally play 4.5 and 5.0 guys at my club -- played a 4.5 last night who is 51, played D1 singles at a PAC 12 university. Lost love and 1. And I played well!
Most of the better guys I play show up with one racquet or a racquet and a mismatched backup. Guy I played last night had an ig extreme pro with some totally frayed multi in it and a half wrap (even tho he has 2HBH) of orange overgrip that looked like it had been on there for six months. His backup was some weird Wilson granny stick that must have been 10 years old. No tennis bag.
News flash: racquets don't matter! Not that thinking about them isn't pleasurable in its on right.
OP's analogy is meaningless. It's like saying boxing gloves don't matter in a fight between an amateur and a professional boxer. Andy Murray enjoys boxing but he isn't going to beat a professional boxer regardless of his gloves.
As far as player development goes, yes, racquets do matter to the extant that they force one to conform to the frame's characteristics or support a player's natural and most efficient and consistent swing path. It's just biomechanics and the laws of physics.
Based on a player's strength, flexibility, agility, hand-eye coordination, anticipation, and timing a given frame will or will not be a good fit.
If you give a really heavy, high SW frame to someone who lacks anticipation and timing skills then the individual will probably end up tearing some tendons or muscles in a futile attempt to muscle the frame into position at the last moment. And if he tries to arm the ball in really hard serves without proper torso rotation he's a good candidate for rotator cuff surgery.
And if you give an open-level player a 9 oz. WalMart Pink Pony frame pre-strung with plastic string he's probably not going to be effective returning 120+ mph serves. The frame simply lacks the mass to absorb the blow effectively.
Furthermore, even small changes in a frame's balance can make strokes such as the serve easier and more natural or make them unnecessarily more difficult. Based on a person's arm length, strength, and ability (or inability) to rotate from the core balance effects swing path and contact point. If one executes a smooth, natural core rotation to contact and a frame's balance is off
for that individual then the point and angle of contact will be off too. Then the player is forced to arm the ball or break his swing for clean contact which leads to inconsistency. It ain't rocket science but it is simple physics.
The only way one can assert that frame characteristics such as balance don't matter is if one can't maintain a smooth consistent stroke from the core. In that case, yeah, frame doesn't matter because you can't maintain consistent form anyway.
I know it's très chic to dismiss tennis gear but if one were to follow the OP's advice and completely ignore the fit between player and frame then at the very least one will have a much less enjoyable playing experience and may well end up with permanent physical damage.
There are strong correlations between frame and physique and skill. Ignoring them, as the OP suggests, is foolish and can even lead to serious injury.
And that's not idle speculation. I know a lot of TT'ers love to amuse themselves with stories about Fedal Wannabes showing up with 12-pack bags and 6 matched frames and then proceeding to be bageled by the apocryphal "Grunge Player with One Old Frame and a Dirty Towel".
But such stories are the exception to the far more common rule.
The fact is the VAST majority of rec players do NOT consider the frame's fit to their body and game. The result is stagnant player development, tennis elbow, rotator cuff damage, and frustration due to an inability to control the ball. They pick up a frame in the big box shop, swing it around a couple of times marveling at how light it is, get strung with an indifferent nylon, and off they go to the courts. They MIGHT get it re-strung once a year...maybe. And as they spray balls around the hot summer court with their worn out nylon and light frame they increasingly arm the ball in a futile attempt to control it. Within months they end up with a stupid magnet on their forearm.
Tennis "pros" don't help much by failing to teach skills such as anticipation, movement, and timing before focusing on strokes. I tell my boys that
good tennis starts with the brain, moves to the feet and eyes, and ends with the core and stroke. Playing tennis like that lets you use a heavier, more stable, and accurate frame which is also better for your body. The usual tennis pro approach is to setup Ye Ole Basket of Balls on the opposite side of the next and start feeding balls to the student.
If you lack consistent form, don't care about improving, have a high tolerance for pain, and the bank account or health insurance to fund medical treatment, then your frame doesn't matter. Otherwise, just like your shoes, it's a good idea to fit your frame to your physique and game to avoid injury and maximize your enjoyment of tennis.
BTW...for those new to tennis and reading this thread, even the OP and those who echo his feeling don't buy the OP's advice. If they truly embraced it then they would save themselves hundreds and hundreds of dollars by buying pre-strung $20 kid's frames from WalMart. But they know it's stupid even for a 4.0 to go out on the court with a 9 ounce P.O.S. and try to compete. And so they don't do it and just flap their gums about the topic.