I think this is a bit overstated. In my experience Bio games are fairly easy, barring the odd difficulty spike. I didn't take those recommended levels as hard gates.
Then we can say it's not well implemented or, maybe, that they are sometimes more easy than they should be, especially in recent times. But the mechanism of the game, in theory, should be this one. Having said that, the reason of my post was to explain (or at least try to explain) why many people does not consider the exploration and the side content an optional content in an open world game, and the reason why many players get angry when someone told them "It's optional, you don't like it, just don't do it".
As I said, I have still to try it because so far I went "near completest" with both of my actual playthroughs (I didn't bother only about some collections like mosaic and bottles) therefore I have still to try one. Maybe that is really true that if you follow only the main quest the game is still enjoyable and you gather enough power/gear/abilities to finish it. And that you will also be able to complete all your companions sidequests. Honestly, I think that in my second playthrough Solas wouldn't be so friendly with my Inquisitor if I stick only to main story choices, because all the approvation I got from him was while exploring, talking with people and finding his artifacts with him in the group. 
Now I am planning a playthrough with minimal crafting and without shards, Oasis, astariums, some boring sidequests (i.e. bring back my Druffalo) and isolated dragons (like EdL ones).. let's see how it comes out 