just saw ur reply now, lars.
thanks for your input.
of course DAWs are sample accurately tight. thats what I meant with “inside”.
if the cpu comes to its limits, a litmus test just recording audio out (mix down is always fine) does not get good marks.
of course u are right I am responsible to keep the cpu load sane. but thats not always obvious, eg. u might be messing with unison voice amount in a fxpansion DCAM synth - well, that is obvious 
however, DAWs do not behave well when it comes to produce a tight midi clock or, even worse, if they have to slave to an external midi clock.
thats why the innerclock boxes sell well.
AR syncs well. however we still have to be aware some user operations can fuck up the timing. to keep the cpu load always sane is basically the programmers job but the user will always find a way to do something unexpected in a complex machine.
its nothing to get crazy about. just have to start&stop a DAW-midi-gear-environment once in a while. and be aware sync might break if we do nasty things.