I agree that we need something that helps us to place more than one block at a time, I mean, we can place blocks very fast, but for huge areas this is such a pain.
In my personal world I have massive projects where I'm constantly terraforming, a tool with the possibility for the player to place more blocks at a time (like the dirt bombs) but more precise, and you can also choose the block you want would be ideal. Of course, you have to be very careful not to make this tool too op, but honestly being able to place 3 or 5 blocks at a time is already a great help.
Also, in the game the options to remove blocks quickly are many and very powerful, for example The Drill Containment Unit, or even the Celebration Mk2 with rockets that allow you to destroy blocks, why not have an equivalent to these methods but for the opposite function? Of course these options for post ML and something more moderate for an early stage of the game.