The choice is between fixing akrasia now, and getting immortality now.

By the Rule of Comparative Advantage, on a planet of billions of people, both can be worked on at once. Since Eliezer -- the person originally addressed -- is not a biologist, there's nothing he's likely to be able to do about senescence, beyond convincing other people that curing death would be great and hoping they come up with something. Fixing akrasia, though, is something that there is at yet no specialised knowledge about, so he has about as much chance as anyone of similar smarts.

Whereas if you first make sure to not die

Ok, that's my New Year Resolution: don't die. Sorted!

I'd certainly take an unlimited lifespan plus akrasia-cure-300-years-later over normal human lifespan + akrasia-cure-now.

I'd take all of it right now. And a pony. (Yes, I'm rejecting the hypothetical. I do that.)