there are two issues related to that:
1) empire and barbarians start with a 2-mission tutorial - in fact, empire tutorial is still not done by mission 2, as you still can't make colosseum and training camp.
There is already an in-game tutorial, having to crawl through many tutorials again, and being unable to build anything at all before having completed the various objectives, is annoying. I think a player should at least be able to make some more buildings without having to complete everything. that way, an experienced player can already start the next objective, and save some time. I understand that the campaigns are aimed at very casual players, and I'm not trying to change the fact, but they should not force a player to do stuff in such a very specific way.
It also hopefully should not require much work from the developers.
But the greatest offender is the next point
2) there is no reason whatsoever to not unlock all the campaigns immediately.
Instead, you can only start by playing the barbarian campaign. Playing that unlocks empire, then atlanteans, and then I suppose frisians.
So, I already played the other campaigns in build 18, and I wanted to try the new frisian campaign, but I can't do it without replaying a lot of stuff that i already did.
If the campaigns had some sort of chronological order or interwined events, it would make sense, but as it is, there is no contact between the various campaigns. They may as well be different continuities. So there is absolutely no reason to not let one play immediately the frisian campaign, and every reason to let them.
And hopefully, this would be even easier to code