Most local newsagents have never stopped selling porn mags. You might not have noticed them, but it's very common in independent newsagents and even smaller newsagent chains. Nobody is switching from the internet to magazines - there's always been a market for magazines. Plenty of older people who don't use the internet still want to access porn.
WHSmith probably don't stock them these days, no, but they certainly used to at one time.
I doubt anyone is switching from the internet to magazines because of the age verification thing. Unless you only want to access material on some particularly iffy sites, there's little to no privacy concern attached to age verification; most sites people are using are owned by large companies who know their business depends on discretion. And if people are still worried, it's not especially difficult to bypass.
I guess whether or not you think it's 'the lesser of two evils' depends on what you think is evil. Any magazine you can buy in a newsagent is going to be a lot tamer than material you can see online - top shelf magazines are basically just photoshoots with naked women with their legs open and grim captions/reader's letters. But that means there's rarely content aimed at women or couples and it's entirely about looking at women posing passively. There is also very little variety in body type etc. Porn on the internet will obviously be more explicit - there will be images and clips of sex acts and it is obviously possible to find content that's disturbing. But on the other hand, you are much more likely to find content online that is made by people of every conceivable body type, every conceivable distribution of body hair and for every conceivable sexuality. Women who like looking at men's bodies are going to find nothing to interest them in a magazine at the newsagents. At all. Women in top shelf magazines are passive objects on a page for men to look at, and that's it.
Magazines are pictures of women mostly being directed, photographed and published by men with no real control for the models. And course, some online porn is equally male-led and the women involved are equally passive and objectified.
BUT online porn will always ALSO include a huge amount of content that's controlled and released by the performers who are choosing what they want to do and self-directing - so, so much online porn is amateur content made by individuals or real-life couples, of all ages, genders, body types, sexualities, preferences etc. There is a lot of material based around women enjoying themselves, to be honest, which is very much not the case in any magazine you'll find on the top shelf of a newsagent.
Some online porn is awful and exploitative and abusive, certainly. But the vast variety means that it's actually meaningless and reductive to talk about 'internet porn' as if it's one thing. It really, really, really isn't just one thing. It varies vastly - visually, ethically, financially. People who are against porn entirely do not, for obvious reasons, actually tend to watch much of it, which means there can be some really odd and false generalisations in their arguments. Obviously I have no problem with people being opposed to porn, but blanket statements about the kind of material on offer aren't realistic or helpful.
I personally would say it was healthier to have a wank while watching a clip on the internet of a couple of fairly ordinary people fucking each other where there's a big emphasis on them both enjoying themselves, rather than a lone woman staring blankly from a page with her legs open like a lifeless sex doll solely there to be stared at by a man and getting nothing out of it. Although there is some appalling, violent, exploitative and harmful porn on the internet, it also provides absolutely tons of the former type of content. But top shelf mags only provide the latter.
Basically, the insanely broad range of material covered by 'internet porn' is both the bad thing about it and the good thing about it. In my opinion, people will always access porn, and I'd much rather they at least had the option to look for content that women and couples have made themselves - and where women's pleasure is at least part of the picture. That is not an option provided by top shelf magazines from the newsagent.