The thing is they can't control the stability of alternative methods on Safari. It's up to Apple.
- Safari + Kagi: you just need a default browser and a non-default search
- Orion + Kagi: you just need a non-default browser and a default search
- Firefox + Kagi: you need a non-default browser and a non-default search
It might not look that much difference but in terms of thousands users, any reduction for users' steps to do, it is better.
The thing is they can't control the stability of alternative methods on Safari. It's up to Apple.