I think it really comes down to what software you need, more than proficiency. Just like you, I'm an advanced user, a software developer, and Mandrake was my first serious Linux.

For me though, software isn't missing on Linux, it's missing on Windows. I rarely need an office suite, and my needs are limited to simple Word/Writer documents and even simpler Excel/Calc spreadsheets, so even MS Office 97 or StarOffice 5 have all the needed features (minus support for XML file formats). The extent of image editing I do is limited to cropping, rotating and resizing images, so even GIMP is way overkill.

On the other hand, the software I do use and like is a pain on Windows. First it's basic text manipulation tools. Things like grep and sed are missing on Windows, and I want to e.g. "replace this line in all files in this folder" far more often than I open an Excel file. I use SSH, which isn't on Windows, and applications like putty are great but don't provide anywhere near the seamless experience that Linux has with SSH. Then there's the desktop environment itself - I use KDE Plasma 5 and find it amazing, having been a fan of KDE since 3.5. I like KDE Plasma overall much more than Windows Explorer, and then there are the individual power features, e.g. I have a button on the titlebar that toggles always-on-top for a window, and I exclude certain applications from appearing in the taskbar because they already have a systray icon.

I use Linux at work, and haven't had to boot Win7 at home since Steam Proton. I've heard that Win10 makes some things better, like it has built-in SSH. But I haven't tried Win10 myself, and at this point it'd take some Windows killer feature to make me switch.