It seems that for arc variants we are looking mainly at convenience, rather than 'essentials' - you can add sketch constraints after initially placing an arc to force it tangent with, or start/end at, any desired feature. So whilst one or another arc tool might be preferred by a particular user, the required functionality can be produced with the available tools - it might be slower, but it doesn't prevent you using a particular approach.
Miles - I just checked in Atom, there is a spline tool (seems to be the 'spline' one form the top of the options in AD).