Moreover, it will be very difficult to judge on one match, and the result is expected as a rule immediately, fans are not patient
True. Fans are the worst judges there are. That being said, judging a national team coach is quite difficult because the number of games is limited, unlike a club where they can see the progress every week or every transfer window. A national team needs to produce results befitting their image in most competitions. Then again, that's the job of a functioning sports association. The bad news is we don't even know if the guys running the association are competent or not, most of the time (at least in my country).
Yes, here we need either a whole tour of friendly matches so that the coach can build a normal tactics of the game, or a few games at the official level within some tournament. Honestly it's hard for me to imagine what a new coach should do when he is expected to produce results in the first game, considering that the players are assembled a week before the national team game. What should he teach them? This is not the national championship, this is the national team level, there is too little training.
The reason why friendlies are not as hyped is because they are not linked to anything. The result don't matter. Winning or losing don't matter.
As the result of the game doesn't matter, teams are more willing to experiment things. Players and teams can practice their own way but friendly match makes them know more about the team they are playing with. For that teams may try to hide their specific strategies and skills in order to use them as a surprise when they play real matches.
If its a tournament they are playing be it a league or knockout, they'd give all they have to win those games.