The issues I see as covering the majority of travel design is, as Windi said, pacing, but I don't think that's necessarily a reason not to, or even having anything to do with, having challenge from the offset. A paradigm of caution is not necessarily a bad one for players to start into, as long as there are sufficient hints to push them towards more aggressive or opportunistic gameplay, just as in the opposite case. The only real difference with expecting little to no resistance and being presented with vulnerabilities, versus expecting vulnerabilities and being presented with mitigation or bypasses, is that (I'd imagine) the prior is a bit more reactive and the latter a bit more active compared to each other. Similarly, the prior's probably quicker to respond to new stimulus, and/or the latter's harder to design cues that don't feel invasive.
I guess another way to term the sense of pacing is "attachment" (emotional?... not quite) or "pivot" (on or by which to adjust perspective). For instance, if you wanted a shortcut to feel like a bonus, rather than just a box on a checklist, I'd imagine there'd have to be a few conditions:
1. You have to be able to reach the bonus based on your own perceptions, interests, and/or initiative, to some extent, rather than it just being tossed in as a quest chain bonus.2. You'd have to spend enough time in the initial condition of travel to have a sort of playstyle in response to it.Exception: when the quest chain is difficult to progress, tempting and challenging you to hurry along in it.3. The improved methods of travel, where possible, should fit the surrounding tools given, and should seem to come from universal emergent mechanics even while creating intended pathing decisions and balances. It should feel part and parcel among the other means of learning or character progression in the area. It both unlocks quicker pacing in other areas (quicker routes meaning quicker gathering, questing, etc., and be a part of that pacing.For example: The objective area is on the far end of a crescent shaped plateau from the quest hub, with a ravine (and a small river at the bottom) running a more direct route between the two, creating a narrowed semi-circular area. Atop the plateau there are numerous dangerous birds who patrol over the area between the quest hub and the objective zone. You can (1) go out of your way a bit to cut along the ridge, avoiding being seen by flying enemies (who will toss you into the ravine for fun if adolescents, likely killing you, or will take you to their nest to be eaten if parents, and will simply attack and probably kill you if youths), but it doubles the time it takes to get back to base, or (2) sprint from point of cover to cover, keeping watch in case you need to hide, etc. This makes it all the more rewarding when you discover that you can repel off the side of the ravine to a path cut into the side, running a more direct route back to base. This path can be seen from the far side, difficult to access, is mentioned by a given NPC on this side, and the rope can be crafted or rewarded. Better yet, you can use the rope to tie yourself to a bird that would have flung you down the ravine to your death or uncomfortable watery landing, simply exhausting it until it puts you down or slams you repeatedly into something deadly. In other words:
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Now, I realize this says little about how difficult mobs should be, or how long things should take. That is because, to be honest, I don't think those issues are of import until you figure out how to make "challenge" fun. As you said, there are no stealth mechanics, nor mob AI at the moment; there's nothing to perceive or gain advantage against. There's nothing to really be optimized that would have much, if anything, to do with the environment of mob type. And gathering and questing don't even qualify as bare-bone mechanics if they're to be considered tools for open world immersion or emergence.
I'm cool with taking a while to reach another town, if there are landmarks, save points of sorts, along the way (not as return points, just as somewhere I can log off and still have an idea of what I've done and what I need to do next on return), and that actual process is fun. Simply keeping your distance from l99 mobs and waiting until they turn around is not that. I want distraction, verticality, gliders if necessary.As Windi said, challenge and difficulty are two different things. The latter, especially, isn't necessarily fun.(The latter being why I hated the idea of unlimited flight in Heavensward; gliders can be used tactically, while anything unlimited and essentially omnipotent has no such need. Now, aerial patrols, limited flight stamina, food, and mount variation could supply that level of interest, but that's not what we got. We got the copy-paste physics-less flight of every other MMO to have flying mounts.)