Indeed. If you hit, energy is no problem. Having Criticals 10, Dagger Mastery maxed and using zealous upgrades, you'll have effective 8 pips of energy regeneration. IF you hit constantly. Making expensive things like keeping up temple strike + wild fangs constantly affordable.
On the question of defense: If you want to, its not that hard to sqeeze in some protection. Eg "watch yourself". -> Even with energy armor set more defense than rangers against physical damage, and more armor than warriors (if u fight warriors for big damage, use elemental upgrades)
The main problem with the defense in this case would be that the Assassin has, at least at the moment, the stereotype of being weak protected. Thus being (even) high(er)-priority target. Thus dying fast, "proving" the stereotype to be "true". Kind of ironic.
E



Even though daggers will max at 12, runes are available for Wilderness, Beast Mastery and Expertise for the likes of apply poison, IAS stances, block/evade stances and pet attacks - and there's a lot of build possibilities there.