How many people practice a forced landing between instructor checks? How many people practice a steep turn? Or a stall? (For that matter, how many instructors practice except when demonstrating ? That can be a long time in between if you're part-time, as I am) These safety-critical exercises are typically tested on a club check-out, and that is what I would ask of a student for the 1-hour flight if I am being asked to sign someone off as a pilot (I have not done any yet). This is probably more important than an "international passenger-carrying flight" which, if this is the choice, is likely to be a typical flight for that person anyway, and so will be well-practised.
This would take 1 hour, and consider how much less would be achieved in two 30-minute flights - on a trial lesson I'm only out of the zone for 10 minutes in such a short flight.