I think there is a false dichotomy here. Accepting a non-universal definition of aikido does not necessarily require acceptance of a definition that hinges on certain traditional practices derived from a particular cultural context. I think it is perfectly possible to derive a non-universal definition of aikido from aikido's lineage, physics, and technical curriculum. If what I am training has a lineage to Daito-ryu through Ueshiba; contains fundamental movements like irimi, tenkan, etc.; and includes aikido kihon waza and more advanced techniques derived from these kihon waza, I think it's aikido, wherever and with whatever cultural trappings it is practiced.
Lineage from Daito ryu and technical curriculum are both totally culturally contextual!
"Physics" is either universal, or also culturally contextual.