I realised only yesterday that my approach to the new module has been all wrong. I thought that since I haven't played properly since Icewind Dale, it would make sense to go through everything that has been added since then in order of its release (Tyranny of Dragons - Rise of Tiamat - Elemental Evil).
The problem is that all the old level 60 content seems to have been levelled up to 70, and the level scaling doesn't work very well. I was willing to chalk up my great weapon fighter's bad first experience to my lack of gear and skill, however when my pet tank and I went into the (now also level 70) Well of Dragons area from Rise of Tiamat with our reasonably well-geared guardian fighter / cleric duo, we still got trounced by the mobs there, even as a team. If my cleric got hit by anything, she would die in 1-2 hits, and some things even one-shot my pet tank. We tried the instanced solo quest to rescue some prisoners and eventually had to give up on it as the boss at the end just seemed impossible to overcome with the constant risk of one-shots.
After that experience my pet tank suggested that we should have a look at the new Elemental Evil content, and lo and behold: that was actually level 60 and allowed us to progress. So if, like me, you have come back to the game for ten more levels and some fun with Minsc and Boo, forget about all the previous campaigns for now - fighting level 70+ mobs is just too much of a pain in the arse at level 60, with or without level scaling. Just stick to the Elemental Evil content to level up - and maybe the early dailies from Tyranny of Dragons (which are in low-level zones).