There is much to say about the problem of closed gardens re: software. We have an incoming cohort of young people that don't know how folders work on PCs, because they've been raised in homes and schools that are funded towards buying cheap software with highly limited architecture: the Chromebook Generation, the iOS Generation, whatever you want to call it. The Eternal Summer warned about in the early 1990s has come to fruition in a way that no one alive at the time was truly predicting.
But you're thinking too literally about the physical form of the devices and the nitty and gritty of the hardware: while the internet was inarguably a better place when 'online' was a rooted location in the household, rather than a omni-accessible place by everyone, the problem is the infrastructure of the contemporary online world. It is basically a crumbling Balkan bomb shelter compared to even the early 2010s, which in turn was considered a blast zone compared to the 2000s at the time. Smartphones are the predominant facilitator of this problem, but it is a problem that extends to massive failures of regulation and capturing of purpose. Home computers are not seen as a mistake, you're misreading the wrong aspect of this deliberately created issue.
There isn't much of a separation from online and 'the real world' any longer, because there isn't much to do online anymore: almost all the websites are dopamine-addiction generators that target every person of every age range, so there isn't any separation of atmosphere that those in their late 20s and up remember from their formative years online. Kids pretty much have Roblox and streaming, both relying on creating dopamine & gambling addiction problems in their youth. What we call online is more or less a graveyard tour now. You post on the dilapidated social media websites that killed off the previous hobbyist infrastructure online, or you read Wikipedia articles controlled by increasingly suspiciously American military base-aligned IP addresses, or you scroll through the utter wasteland of AI-generated 'media/content' that has completely wiped out any incentive for small-scale human creative ingenuity that the internet was great for. Reddit and Discord have both absorbed the previous two decades of fandom/hobbyist/creative communities, and made their information increasingly difficult if not outright impossible (in the case of Discord) to store, search and archive, which has been catastrophic for the the idea of the internet as a home base for specific, particular and relevant information that bolstered all sorts of lifestyles and ideas. Search engines have been wiped out: while they still exist, they have the function of arcade claw machines - they only pretend to pick up the information and dangle it in front of your eyes, and then they drop it back into inaccessibility, if they find it at all.
The online infrastructure has collapsed because it is more useful for increasingly right-wing, war-hungry governments belonging to a certain hegemony, one that requires angry, info-starved, dopamine-fried and ultimately compliantly stupid individuals to ignore what they see in front of them. This is intentional: the only super highway of information allowed to remain is one that allows people to post about their favourite franchise IP & why the world should preemptively nuke China, creating walking foot soldiers for conflicts we haven't seen the origins of yet. Just endless anger and for what?
This problem has been largely facilitated by smartphones and the way that modern app software works, frying the minds of nearly all who use them, but smartphones are only one facilitator of a problem that extends far beyond the literal hardware of how we access online. We access online, and then find that there is nothing left to access. The era of the internet up until roughly 2016/2017 was better than what we have now, simply because while there were still smartphones around, the internet that could be accessed via smartphones or PCs was still largely fit for purpose, even if the issues were creeping in at that point.
That is the larger problem that we have to be frank about. The differences between PCs and smartphones are not arbitrary, one is clearly worse for the online ecosystem than the other by virtue of one allowing instant access from the dumbest people alive & generationally-incoherent old people, but it is only a small slice of the issue.