Should I evolve my Chansey?

I live in an area where Chansey is quite rare. I managed to get two of them during the valentines event, and have 60 candies. Without the valentines event, it will be a VERY long time before I find another decent Chansey and collect enough candies to evolve it.

One of them was garbage - the other is good - LV20, 80%IVs with Chanseys best moveset - Pound/HyperBeam.

If I evolve it into Blissey, I have very high odds of having a crappy moveset. Is it worth it to do so?

I intend to use it primarily as a gym defender and to use the high HP to practice dodging (which I suck at - I'm OK at dodging quick attacks, but can't seem to dodge charge attacks).

I am somewhat new to Pokemon Go (only picked it up in late Jan.)