I don't know... I really think the way people talk about this doesn't really do justice to other stats. Characters that immediately come to mind for no speed primary arrow:
GAS - protection
Jolee - possibly CA
B2 - CA or protection
Magnaguard CA or protection
GMY depending how you use, offense
Holdo CA
R2D2 speed health offense or protection, use dependent and what mods you have available
GK just wants a great tank build
If you have a 20+ speed offense arrow, you should probably be using that somewhere like on Droideka. Almost all 20+ speed secondary arrows except defense primary now could theoretically have a use in a particular build. This really depends on your mod depth though.
It's not like it would make sense to put a 25 speed offense primary arrow on a toon with a main speed set averaging 15 speed per mod....
Also, if you have 20 speed secondary arrows with great synergy, consider calibrating