But that's a complete disservice to the actual point of why people like MGS.
Yes, but also no. A big part of Metal Gear's appeal has always been its tendency to whiplash between a military thriller and a robo-kaiju ghost story. Remember that this is the series that will spend 2.5 minutes going over
all the custom modifications of Snake's 1911 in the same breath that it will tell you that
an AR pistol with unlimited ammunition makes sense.
Also worth noting is the time frame of these games' release. 1998 was the first time that "realism" went mainstream as a design goal outside of dedicated simulators, with Rainbow Six, Metal Gear Solid, Half-Life and Thief all releasing within months of each other. Once again, MGS is not really realistic, but in the wake of Quake II, even small concessions like requiring the player to navigate an enemy base by means of subtlety instead of firepower was a large step away from the previous norm. Yes, realism really was a fucking selling point for MGS1. Compared to the rest, however, Rainbow Six essentially kicked down the door and screamed "I'll show you what realism looks like! It looks like 'you're dead, your wife's a widow, and your kids are going to grow up without their father, all because you turned right instead of left when you went through that door!'"
From that standpoint, then, I can see the logic of making a Tom Clancy stealth game: the genre had been proven, realism was on the rise as a marketable feature, and the thematic comparisons and contrasts between Metal Gear and the Tom Clancy brand set them both together and apart, the perfect place to compete from. All of Tom Clancy's works of fiction were ultimately thrillers, but the devil is in the details: compare any Tom Clancy novel to its corresponding movie, and you can see how much is lost without the technical autism. From there, the path should be clear: remove the batshit, ramp up the autism, and sell Splinter Cell as the hardcore alternative to Metal Gear.
This, however, is where they fucked up. While Splinter Cell did remove the crazy bullshit from the story, the gameplay was ultimately just as fundamentally silly as Metal Gear's, leaning on the Tom Clancy brand to give it an air of believably that it didn't earn, and setting a trend that would continue until Siege did away with single-player campaigns entirely. The Clancy brand stopped being about "this is how shit works in the real world", and instead became "this is a plausible, believable scenario". But remember what I said about the Clancy movies, that without the technical angle, Clancy's works are just everyday Hollywood blockbusters. By discarding the commitment to realism, a critical piece of the puzzle has been lost, and the brand has been adrift ever since. What we see now with Quarant-er, Extraction and XDefiant is simply the next turn in that aimless wandering. When Siege went multiplayer-only, it also started moving back towards that technical, realistic angle, but as I've already noted, it abandoned that at right about the same it started becoming popular, meaning that now the Tom Clancy brand has come to mean "muh skill-based matchmaking and memorable characters with unique abilities". If the Clancy games were aimless before, it's now completely mutated away from anything resembling its roots. Even CoD hasn't fallen that far.
