It was still much more consistent than things are today, though.
With respect to toolbars / coolbars specifically, one thing to remember was that those weren't kept for Office/IE use only, but rather shipped as reusable components ("common controls" etc), and so other apps could and did pick them up. Indeed, well into late 00s, the common fashion for Windows apps was to try to look like the most recent version of Office wrt menus / toolbars.
Also, I do recall that those apps which tried to look flashy with fancy custom styles etc were often perceived as unprofessional, and quite a few people (myself included) deliberately avoided them where possible - and it wasn't difficult to do, with natively styled alternatives readily available. I distinctly recall my own late-90s Windows desktop, and it was very consistent.
IIRC most of these controls only shipped in comctl32 much later than they launched, and comctl32 came with the OS which had many-year upgrade cycles. So in practice everyone invented their own because they didn't want to wait.
I'm sure people who care could make a consistent desktop, but our memories differ on how popular that was. The theming craze was a 90s thing, so even when apps didn't roll their own brand like MS themselves did, apps often let you apply custom themes to change the look.
In theory it's easier than ever to do that. You could create a browser extension that used user stylesheets to restyle websites to have a consistent look and feel. People make that effort to build ad blockers but not to build consistent looks, so I guess there isn't that much demand.
With respect to toolbars / coolbars specifically, one thing to remember was that those weren't kept for Office/IE use only, but rather shipped as reusable components ("common controls" etc), and so other apps could and did pick them up. Indeed, well into late 00s, the common fashion for Windows apps was to try to look like the most recent version of Office wrt menus / toolbars.
Also, I do recall that those apps which tried to look flashy with fancy custom styles etc were often perceived as unprofessional, and quite a few people (myself included) deliberately avoided them where possible - and it wasn't difficult to do, with natively styled alternatives readily available. I distinctly recall my own late-90s Windows desktop, and it was very consistent.