I actually only see the preseason matches played by European teams just for fun, especially those who tour Asia and have a series of matches. They can field new players for the preseason match, but not with the actual game tactics. Because the tactics will usually still be adjusted to the strength of the opponents they study. Preseason matches are more about preparing the players' fitness before the official competition starts.
Preseason game is not one to take to heart as some people does so I prefer it as fun just like you did said because of a truth these teams will not be putting in all of their very best, they do not really stand to gain much from the game so why stress much if not to test strategies and tactics which will eventually be modified. This is why when I see a team mostly the big ones winning almost all of their preseason game, I just see it as them exhausting themselves whereby they should be resting awhile and bring the actual performance to the main season.
Preseason matches are only important for young players and reserve players to prove their quality, otherwise I don't think it's as you said, even the team's strength doesn't come out fully in preseason matches, even some of a team's main players tend to rarely play and that's done to avoid injury or they prefer to rest before the competition starts, so this is indeed the team's agenda that must be fulfilled so there is no reference to the preseason match.