"The decline of the game as we know it...."
We are not all the same, and I don't think there is a universally known game, that 'we' all know. We all have come to the game, and currently participate in the game, from different perspectives and for different reasons.
I don't think the game has been terribly diminished by technology, per se, for the average golfer. If that average golfer enjoys playing with similarly inclined companions for pleasurable friendly competition, or just exercise and fun, golf as a game is not in decline, IMHO.
However, if golf courses are designed to frustrate, penalize and provide hurdles that are targeted to challenge only the best players, and discombobulate the average players, then I can't see how it could not decline in participatory numbers of people seeking such pleasure or affording such. Yes, as David says, there is nothing like hitting good shots with whatever equipment - old or new. And, you can do that at a muni, range or lavish CCFAD, etc. Access to where you go is the only limitation on that front. If you know people that would like to play golf more in companionship, but aren't about to pay a fortune to do so, it is not conducive for you to participate either.
But when it is a constant race of marketing technology that extends yardage, minimizes mishits, and feels less harsh on the body and hands, it tends to cost more and more to keep up. To go along with that, the effort to provide 'more than just golf', with ancillary things like golf assistants with mellon scented towels, non-golf related aesthetic landscape, and overly lavish clubhouse facilities, are things that can cause the participatory decline in availability to play the game on the cost front. Tim Weiman's old saw: "people want to play more, not pay more" holds true, and does have a bearing on the notion of decline, if people are leaving the game due to cost.
But that is a mixed bag. If numbers of people are leaving golf as a game to be widely enjoyed, and if numbers of rounds per capita among golfers is declining, then perhaps cost to participate is one major cause to consider in such a definition of decline.
If decline is deemed to mean, the game as purely an activity of enjoyment is declining; then I guess it is down to your own definition of whether you are enjoying it more, or less. If we are all saying we are enjoying it less as an activity, then there is deep serious trouble. I don't think we are there yet, on that score.
So, for my understanding of whether golf is in decline, I will define it by the numbers of people playing, taking it up, or playing as much of it as they always have per year, etc. If that is declining, I'd look to Weiman's observations.