Difficult getting from one town to the next, where any monsters could easily kill you, and required very careful analysis of mobs' movement...

Sounds a lot like the trek to Jeuno in FFXI. Yeah, I'll never forget the first time going there.
I loved that challenge and I agree this game lacks challenge in many areas.

BUT, I think that is why it is so successful. It has so many players, and the casualness of it is what keeps many players playing.
Most of the game is easy and simple and people can enjoy it.
There is some content aimed at people who want a challenge too.

If they were to increase the difficulty of this game to make everything challenging for everyone, a lot of people would complain / quit.

I personally loved the challenges that FFXI had, but I think it would be very efficient to carry it over to this game. Unfortunately.