Is the issue the low # of rolls for tempering…

I agree that tempering is too powerful.
That said, even if less powerful, we are talking 2 extra affixes on items that sadly only have 3 affixes. It will always feel mandatory.
I don’t think it is a problem that they feel mandatory.
They do seem too powerful compared to other sources of power in the game though.

Nor is the low number of rolls an issue.
Tbh, if there are any issues with tempering, it is that the affixes are too specific.
Instead of 20 different affixes that increases AoE size, just have 1 such affix. With coefficients for each skill that affects how much they scale with the affix (like if you get +20% AoE size, a skill with 0.5 AoE size coefficient gets 10% increased AoE size).

Broader affixes would make it much more likely you get an item that can be used for something, even if it isnt what you hoped for.

Don’t make it possible to get extra rerolls through sparks etc. That would destroy the system.

Not a bad idea, the game should facilitate more hard choices.
Proper affix balancing would be even more important though.

And items should drop with more affixes from the start then, if tempering became more optional.