Flying if its possible
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I don't think that is really an issue. The game doesn't give every player everyone else's buildings, roads, etc. If you like a player a bunch or set up a contract with them you will still only get bits and pieces of the infrastructure they set up in their own game. No matter if you have 30 strand contracts.. you're still going to be doing the vast majority if the building in your playthrough as will everyone else.
TLDR: What is yours is yours, what is theirs is very rarely in your game and vice versa.
I agree with you. This trainer is not going to ruin the "online" aspect of the game.