It looks like most of the margin differences you complain about are due to icons not filling out their square canvas/bounding box depending on the depicted object. This is generally how icons work, unless you go Android and slap a circle/squircle background on all of them.
Which isn't to say things shouldn't be better, of course.
There's currently a big multi-year community effort underway to overhaul how KDE's visuals are made, including adopting a modularized design system, Figma/PenPot and a new theming engine (Union) designed explicitly to serve the designer's needs. Along with the KDE Linux distro these are our two main next-gen efforts where we want a capability step change in our practice and product.
Which isn't to say things shouldn't be better, of course.
There's currently a big multi-year community effort underway to overhaul how KDE's visuals are made, including adopting a modularized design system, Figma/PenPot and a new theming engine (Union) designed explicitly to serve the designer's needs. Along with the KDE Linux distro these are our two main next-gen efforts where we want a capability step change in our practice and product.