You raise some good points, and at the elite end - the real top end of ABBL and other leagues across the world - you might be right.
However, for the majority of teams - and for most teams in say D3 and most of D2 etc, I would still highly recommend 1on1 training to start with. As we agree it yields the highest TSP gains, it is the quickest and easiest way to raise the value of your individual players and of your team. Definitely starting out, I think you'd want to get 5-6 18 year olds and run some 1on1 (maybe some JS thrown in too) and then sell down to 3 main trainees that you then focus on finishing.
Once you have an established team with a maxed arena and are thinking of taking the next step though, it is worth considering how your team will look 5-10 seasons down the track, and optimising your training on your star trainees is worth looking into. Not something I've thought about long and hard personally, I just wing it week-by-week for the most part, but if someone else wants to come up with the answers I'm happy to listen.