With all due respect to @David_Fergen , I don't think the guide does anything to answer your question. In all fairness though there are a lot of factors to consider and I think you'd be best off exploring in some depth your requirements with a well informed implementation partner or perhaps the Qlik scalability labs team.
In theory up to a point you could certainly scale both implementations easily enough, the key difference will be the elasticity of the K8s deployment and the impact that may have in terms of your infrastructure running costs. If you aren't already running K8s, and more ideally a platform such as OpenShift to make running it in production something less than a nightmare, the time and costs associated with coming to grips with the technology are quite high.
I've not done a scalability comparison and don't ever expect to have access to the resources to do so (without significant sponsorship at least) but in theory I would think that you scale out better with a K8s deployment provided you architected it correctly and were capable of running it well. There should be no reason you couldn't scale up a windows and K8s deployment equally.
From my perspective the advantages of K8s are less about potential scalability but more about the hybrid-cloud / multi-cloud advantages that it offers and the potential for savings on infrastructure costs provided you do achieve enough scale to have those costs overcome any ramp-up costs associated with adopting the technology. If you've got a running production kubernetes platform that you are happy with then I see no reason not to do it as you'll already have absorbed the sunk costs of setting it up, however if you haven't then scalability would be a minor factor in my mind in deciding which platform to go with unless you are at the extreme edge of scale requirements. Remember also that depending on your requirements there are a number of ways of addressing different scalability scenarios with standard Qlik Sense on Windows and that Qlik is very focused on delivering all new functionality to it's SaaS platform ahead of anything else.