It's a prewritten adventure. Whatever they've been saying about magic items, Wizards have not borne it out with their published material.
What part of "optional" did not get through? They gave away that many magic items because the game is set on Faerun, which is swimming in them and can thus expect all the npcs to be similarly equipped.
If you wanted to play Conan, however, less is more.
I like that there isn't a set "magic items by level" concept. It allows me to craft my setting to fit my expectations, not kludge the entire world economy around the existence of +1 Swords.
Lost Mines of Phandelver takes you to level 5 and gives you 3 magic weapons, a wand, a magical staff and 1 bit of magical armour.
So six pieces of magical loot for a four man 5th level party. Seems about right compared to, say, Pathfinder, where if a 5th level party has less than ten magic items they're seriously underpowered.
My issue is twofold:
1. The DM has taken away half of our resources by having an NPC steal our gear when we got killed (a trustworthy NPC who had never given any sign of being a thief) and isn't allowing us to get any of it back.
This is your GM being a dick, which is not something the rules can fix for you.
2. As a starting character I don't get to have all the things I associate with being an experienced adventurer: I can't afford spare weapons, all the miscellaneous bits and bobs, better armour than I start with. But I'm joining party where 3 members will have this money and the magical items and 4 characters won't.
Hey, maybe... I don't know, they could share the wealth? This is not a problem that can be solved on a rules level. This is a group, real life level problem.
And a level 3 or 4 character? Against Wraiths, which take half damage from non-magical weapons?
Yes, because by sixth level you're attacking twice per round, which thus averages out to normal damage. Not to mention that the Paladin will be doing Radiant (which does not weaken), the Rogue will be doing 3d6 of sneak attack (seriously, sneak attack became like a
thousand times better, archer rogues are devestating), the Barbarian will be doing three attacks with bonus damage, your Fighter is doing various tricky stuff, your Monk counts as magical and is doing Three~four attacks per turn and thus chewing through them like a woodchipper, etc etc.
Even 4th level characters should be doing more than enough damage that resistance is not a problem, considering a Wraith only has 67 hit points. So since average fightery types damage is about 8 points per hit, that's about... 16 hits, or four turns versus an regular party (considering some will be attacking twice, doing bonus damage, using magic, etc).
Plus a Wraith is a CR 5 monster. It's
supposed to be a major challenge for a group of level 4 characters.