The lack of account wide achievements is what prevents me from being willing to invest time in my other characters.
The transfer of achievements to all my characters whether earned or not is what would prevent me being willing to invest time in my other characters.
What would be the point of my playing those characters through the game if they were already credited with having done it all the moment they were created?
Your position represents primarily those who roll extra characters in order to give different options in "endgame", which they wish to rush those characters to as quickly and effortlessly as possible, while my position primarily represents those who roll extra characters in order to play the game fully with them over a period of time and with full commitment to all their characters equally and individually. I honestly think that ZOS have done a good job of balancing both our positions so that there are some things that are account-wide such as collections, champion points and now skill points through the crown store, as well as with some things that are character-specific like most achievements. It's a fair compromise at present in my view and doesn't need changing.