I've never seen an ad on Windows, and mine came with the laptop - I believe that's because I disable all personalization features when first setting up my laptop. Anyway, the old school bar has been available as a built-in "feature" for probably around a year, you can select "Combine taskbar buttons and hide labels: Never" in the taskbar settings.
I'm not sure I would describe it as revertible to the old style at all.
What you can do is change the alignment to the side instead of the centre.
There are still quite a few annoyances in the taskbar/start menu/system tray area, things that feel like they have changed for the worse.
most of my annoyance comes down to the increased telemetry, ads everywhere, and the overall look of the system, dumbing the UI down basically.but I do have concerns of them breaking compatibility with older apps as well.