Perhaps. Maybe it is like a plane that is consistently losing altitude. At some point that becomes unsustainable. My reasoning is as follows;
The only business that makes a profit in all of the Alphabet companies is search advertising. Everything else lives off the excess thrown off by search. Which isn't to say that they don't have other large business revenues, just that they don't make any money. Youtube being the poster child. And it consistently skates the line between slight profit and slight loss and never comes close to the margins that Google would need to make it an independent P&L center.
Then, the profits on search ads have been falling, for at least a decade now. Inside Google that was reflected by cutting costs and deleting benefits. Killing projects that weren't profitable and shedding businesses that weren't ever going to be profitable. Then it started showing up by more an more ads on things. The sad truth is that if you are getting less per ad, you can always add additional "inventory" and keep your numbers looking good. The cost has been that search results have suffered.
I worked there 4 years. Got a good look inside the sausage factory as it were, and frankly the huge profitability of search ads in the beginning instilled a culture that literally couldn't see operational efficiency as a thing. I don't think they will be able to shed that culture before it is too late. But what is too late?
Well if you can't find a business to cover the profits that are evaporating from search, you have two choices, cut costs or monetize more. The former makes you not a 'fun place to work' and cuts into recruiting and productivity, the latter cuts into market share as your product is less and less differentiated. Say what you want about Marissa Mayer, she did get that aspect of Google. And if you're old enough to remember Alta Vista, the "premier" web search engine from 1995, you probably watched how. when it lost its edge against Google, it went crazy with advertising to try to pull up from a collision with bankruptcy.
One need only look at two things, the amount of money Google is increasingly paying to people to send search traffic to it, and the growth of "search engines" like Duck Duck Go which use Bing results to populate their SERPs, to see that Google is losing here. Those costs further erode profits and market share.
And when that erosion hits hard enough it becomes self sustaining, like a dam that has a small crack which becomes a torrent.
A number of people I know from the search business, former Googlers, some who are still Googlers, investors, media, and engineers I met while working on building and deploying the Blekko search engine with their founding team, are all following along as well. I don't think one of them thinks Google is "doing well" at this point. Sure lots of people were skeptical back in 2012 when I started saying it, but now pretty much everyone can see the pattern. Tick, tock, tick, tock.
Now don't misunderstand. We would all love for them to pull out of their current trajectory[1], but temper that hope with observations that they are not. I have seen too many "Gorillas" (in the Geoffrey Moore lexicon) go down this path to have any reasonable expectation that they will survive it. If they follow the classical Silicon Valley playbook, they need to finish their masterpiece "Grand Headquarters Vision" so that they leave behind a tomb for others to remember them by. I have some great memories of TGIF meetings at Google which were held in Building 42, which had been the centerpiece of Silicon Graphics view of its rightful place in the world. I tried to tell them to be respectful of the ghosts that walked the halls, but they didn't understand what I was saying.
[1] Well to be honest a couple of them would be happy to see Google die but I'm not one of them.