Yes, the double jeopardy SP nerf should be ended. Surplus is to stop you from progressing in miner ranks too quickly. Field fatigue should only limit production, not progress too. You can be a weekend warrior battler, but if you try to do all your week's mining on saturday and sunday...well...the system will eat you alive.

You should get full SP for mining a fatigued item fail.

Unfortunately field fatigue is tied in with the stats that determine your success--that is, damaging the item because you didn't have the stats or power is the same system as damaging the item because you are fatigued. Therefore, to change it would require redoing what "success" means.