Ahm... I think, condition loss depents (on new training) on the fitnesslevel - one of my defenders (180% fitness) lost a lot less condition on 20% drills in comparision to old training pratice match.
old training: ~18%
new training: ~12%
If your player is below 120%, I think, it doesn't matter, what kind of drills you use. You only check, that you don't use drills with more than two times the same attribute: f.e.: skill drill, 1on1 finishing and stop the attacker/slalom dribble/sprint do have all "dribbling", so I just try to use only 1on1 finishing and slalom dribble on one session.
If the player is above 120%, my experience says, that's better to use a hard session (should be 15% or more) for better %-condition loss-ratio.
First, I don't think, that players performance is worse, if he has, let's say, no % in fitness like my ST. Only thing is, he lost more condition than other players during a match.
Second, I have to say yes. Let's take my ST for an example: If I make a session with only one drill, I use "press the play". I need around 6 or more session, that he gain 1% in bravery, marking,...
If I do the same with "pass, go and shoot!", he will gain at least every second session 1% or more, because he can use speed, passing and shooting.
But... my ST will need more sessions, because he isn't a fast trainer, 24 y.o. and 135%. This all are things, that slow down his gaining.