Different attacks have different animation speed which is not bad in itself. For some attack though the animation speed is so low it drastically impacts the skill performance and diminishes the impact of numbers tweaks.
In endgame environment you are often surrounded by multiple enemies with cc abilities and a lot of your slow attacks get interrupted before going off. This applies not only to select casts but also to WPS: even with attack speed capped skills like Belgothian Shares and Necrotic Edge can often be interrupted and even miss the target because the impact comes so apart from the start of the animation.
In here you can see that in period of 10 secs Forcewave spam completes 30 casts, DEE - 38 casts and Stormfire - 44 casts.
This is the main reason why Forcewave is only competitive for phys and fire dmg types where it has huge support from the itemization (in case of fire it barely does half of the build’s dmg).
Consequently chaos Forcewave is a joke of a build compared to phys and fire and other chaos builds despite dedicated weapon, huge sheet dmg (100k flat average under the buffs) and all the qol included.
Other skill that comes to mind first is Blackwater Cocktail:
BwC has a lot of support from strong items but i don’t remember last time i saw a BwC spam build. Chances are slow animation has smth to do with it.
If animation speed change is not a taxing process i think it can be a valuable tool in balancing. Recent changes for some of WPS made 2H AA builds much more fluid.
it always confused me skills had different speeds to the point of being “detrimental”/incurring a subpar dmg loss on some skills