why doesn't Timmins have more value? He's a two-way defenseman who just put up over half a ppg at 24 years old and is very affordable for the next two years and expires as an RFA.

Extensive injury history with long term absences

So literally the same reason as Nick Robertson minus the r height issues?

Injury problems and his ceiling seems to be that of a 3rd pair D

There is no real risk. Not much invested in him, let's see what you have.

but if he put up over half a ppg (yes a small sample size) at a young age and is a two-way defenseman, wouldn't that suggest more than a bottom pair defenseman?

No, points aren't everything and the sample size is very small, anyways, Timmins is 24 which is (normally) close to the end of a development curve, I wouldn't expect big things out of Timmins