There is no 'right' way to progress. There is a suggested way, but it is not the only way. I used Troll armor in the Plains by choice (before Fenris was added) and did fine. I am sure there are people that can make the Plains work in even lesser armors.

You can, in fact, get all the way to the Plains without killing any Boss and do fine (Moder is the first boss that actually prevents progression because of the need for tears).

That is one thing I like about this game (and something that was more common in older games than it is now), you can go wherever you want. You may not survive long, but you can still go there.

These days it is more common for games to do what the OP writes and 'funnel' players along certain paths, while giving the illusion of free roam. But then again I understand why developers do such things to avoid the 'its too hard' faction.