Having said that, I'm still a die-hard Xfce user, and until someone makes an xfwm4-like Wayland compositor, and ports (at least) xfce4-panel and xfdesktop to Wayland, I'm not gonna switch.
Edit: ok, looks like there's Hopalong (https://github.com/iridescent-desktop/hopalong), so we're part of the way there, even if it's pretty new.
If you right click the title bar of any window, to open a menu, from which you can select resize.
But I just live with it. Honestly I don't resize windows that often. I either use the window's natural size, or maximize. In the 18 years I've used Xfce it hasn't been a big issue for me.
For what it's worth, it works very well one-handed on laptops, this is how I've used it for years and I greatly prefer it. The click target, that is the area you have to aim for with the mouse cursor, is much bigger than even the most absurdly thick window borders, so I find it much easier to use.
Have you tried changing the window title / border theme in Settings / Window Manager? There are a few themes with resize corners only provided on top and bottom, and with left/right borders 1px thick; you might have switched to that and had the frustration. But there are definitely a number of themes with comfortably thick border. (My preferred one is Smoothwall.)
Even though it has been 7 years since the initial report and the issue is still very much active, the assigned dev says it's a low priority to him. If you know how some FOSS project still work, there's very little hope for a change anytime soon.
There are lots of stubs of news out there on the web that xfce development may head in that direction, potentially moving from xfwm4 to mutter, so fingers crossed.
(I am definitely an xorg apologist but ... that's because it does what I need, painlessly. As/when wayland can, I'm good to move, especially if the majority of development is taking place there. We just never quite seem to reach that point.)