I'll get straight to the point; please bring back those "Legacy Achievements".
For the "Miner" achievements; just add a "Recycle Box" or something like that where you can trade in minerals for some crowns, and let the recycled minerals count towards the achievements.
For the "Walk it off" achievement; just change it so that you have to revive someone while you have only half a pip of HP left.
This topic has been discussed time and time again. Those who achieved those achievements still have them, and those who are newer knights or never achieved them don't see them as achievements in-game.
If you are talking about Steam achievements, they would need to either bring back the obsolete methods of obtaining the achievements, or delete those achievements from Steam. One would be a slap to the development team, the other would be a slap to those who achieved them. If you want to take it up with Valve on having a new kind of "legacy achievement" system, ask them about it. They are a third party, and Three Rings cannot change their software on a whim.