Chain challenge SP farming (exploit?)

I finally started to complete theses and the beginning ones are extremely easy. Then I noticed on normal mode, I'm still earning 3 sp per kill on my first runs. If you complete it and go back, it'll be reduced to 1 sp per kill.

So I tested something and it works. If you make it to the last stage then surrender, you still get all your sp up to that point. Then it doesn't count as completed, so you can go back and repeat it.

I'm aware you can accomplish his in tempest trials, but those you actually have to try for. I can easily blow thru these normal missions. Also just realized lunatic gives orb rewards.

Combine this with double SP weekend for tons of easy SP.