Some things must be permanent and unchanging like swordsmen fighting in front row, because it just makes sense.
The same logic can be applied to the battlefield in GWENT. Just because a warrior uses a sword doesn't mean (s)he needs to be in the front lines -- and neither do archers or other ranged units need to be in the back every time. Wouldn't make sense if they did.
As for rows having set effects vs. cards having row-based effects, I think both options have their pros and cons. The former I have no experience with but I like the idea.