i played anno 1400 this year and i concur the combat stuff is pretty dire. The ship combat is fine if a bit simplistic. But land battles is a both boring and a mess. one mission in the story campaign was more then enough for one play through thank you.
interestingly i played anno 1400 partly because i wanted to get anno 1800 but wasn't sure about it. The settlement management stuff itself is simple, yet satisfying. Sadly i didn't have time or skill to make wonderful cities. just boring square ones.
Will i get anno 1800? maybe, i'm in no rush after getting a rough idea of the mechanics and the style of play i felt that put off by them by the end. part of the problem is you need to set up supply chains and it got really tedious as different islands provided different resources and you shipped good/raw materials around to make things work. i suspect the additional DLC will make this even more complex/tedious as it adds another layer to things.