1. The article claims that Microsoft Office 365 is $100 a year. In reality it's about $70, home license for up to 5 users is $80.
2. The article does not mention that every Office 365 user gets bunch of additional services. For example, a tebibyte of space in Microsoft OneDrive for each user, 60 Skype minutes per month, etc.
3. Each Office 365 user can install Office apps on 3 devices: his phone, tablet, and computer. Office apps are available on Android and iOS as part of the package. $70—$80 a year price tag includes not only Windows apps, they work perfectly fine on smartphones. Personally I make grocery lists in Excel, open them on my phone, fill my shopping cart with items, and track how much I'm going to pay or if I'm eligible for coupons.
4. I'm not aware of any decent OneNote alternatives. I researched it some time ago because I desired to self-host my notes. There are pretty much no comparable open source or free cross-platform apps which can work with notes in cloud or on a remote server from your mobile device. With OneNote all of my notes are available on my mobile devices. I strongly believe that OneNote is one of the best apps Microsoft came up with in recent years.
If you look around, you can see that 1 TiB of cloud storage alone costs $100 (Google Drive) or $120 (Dropbox). Office 365 offers not only that but also quite possibly the best office suite on the market for $70 for 1 or $80 for 5 people.
Note that so far I have not touched the question of quality of software at all — only the most basic functionality and packages. Microsoft Office is the most popular office software package for a reason. My exposure to open-source office packages is limited but here is at least one dealbreaking example. I tried recreating my spreadsheet for tracking caloric intake in LibreOffice Calc. It was extremely painful — among many other features Calc does not even support tables like Excel does.
I use another software package mentioned in the article — Kaspersky. I'm going to assume the author is talking about the package I'm using — Kaspersky Internet Security — since the price is stated to be $40.
Like with Office 365, KIS is not only an antivirus. It's also a firewall, parental control tool with a list of inappropriate websites, an adblocker, etc. It provides quite a lot of functionality, some of which, frankly speaking, should be in Windows itself. For example, KIS can autoupdate software.
Like with Office 365, article does not mention that $40 buys you a license for up to 3 devices. KIS is also available for Android and macOS.
But overall, an antivirus is not necessary in modern Windows system, so you may skip on these $40.