It depends on the qualities of the practitioner.
Qi is not only a concept.
Awareness is important (and qi is awareness-related).
One could try to define a law as follows :
When all other things are constant,
and awareness is higher,
the massage will be better.
Which is of course just a concept (for one cannot keep things constant)
Shiatsu has some nice diagnostic tools, and some tricks to work with after diagnosis.
Apart from that,
diploms are b u l l s h i t.
most differentiation is b u l l s h i t when it comes to effectiveness.