Below is a bunch of comments as I read through it, then I can back to write this. There's a lot of good stuff here. Don't take away I dislike it because I have some negative comments. On the contrary it looks good and I hope my critique can make it even stronger. Most of them are minor tweaks. The only thing I thought was a real problem is how high-magic the Magus is - not in terms of volume but in terms of ultimate flexibility. I'd rather see that curtailed but that may just be a table difference in "low magic" preferences.
Anyway, onto the read-through:
Fey Ancestry: Sleep magic is more powerful. Not what I was expecting for a low magic game.
Races: Various debuffs without anything to bring them back in balance with the other races. When taking away I'd give something back.
Classes: Good non-magic list of PHB classes. Here there was a swap to remove the "Use Magic Device" for Rogue (Thief) to keep it balanced.
New Bard: Bolster Morale is a weak version of the Inspiring Leader feat that gives les HPs and is only using once per long rest instead of per short rest. It scales very poorly, it's mostly a ribbon. I'd consider just giving the Inspiring Leader feat instead.
Not sure how College of Lore helps contribute in combat to be on-par with the other classes - barbarians and fighters with extra attack and rogues with sneak attack, and that's if for classes. Now, I'm personally okay with that myself but it's a break from D&D's "combat takes a lot of wall time so everyone must be able contribute and get equal spotlight".
Magus: More spells known then the sorcerer, able to cast multiple spells of high levels unlike the PHB classes, d8 HPs, metamagic (though delayed), huge spell lists to pick from, able to spam low-level utility spells like shield all day long.
I don't know if my DM in a normal game would consider this balanced vs. the other casters. It's got it's limitations, but it also has some places it's definitely better than PHB casters.
One thing I do like is that you don't get back all of your spell points every day. 5e has very limited multi-day attrition rules, with exhaustion and HD beign the only ones I can think of. This has a lot of the low magic feel for me that even if you can do big magic, you won't waste it on small things and be cautious in it's use. This is the Gandalf feel and it comes across well.
I'm surprised that if you were going to include a low-magic caster, it wasn't based around the warlock. They have a lot more hedge-mage vibe going with particular invocations that they can't change, and limited flexibility in casting due to having few slots. It might be a better chassis for low-magic casters huge spell lists, avoiding slot limitations, and metamagic.
New Ranger: "Loyal Companion" gives you a normal dog that never scales up. This is a ribbon ability at best. True story: my last ranger had this, but he just bought a hound from the PHB equipment list and had the right skills we said it was trained.
Feats: Just a question - you've got XGtE classes, I'm interested in the choice of not including any of the racial feats.
Also wondering about not allowing Mage Slayer from the PHB. It's non-magical, and seems like something that would be developed by those fearful of magic. It wouldn't come up as much, are you worried about it being a trap?
Resting: Nice and gritty. Good.
Encounter advice: Good. Though less encounters per day favor those with long rest recovery, which at this point seems mostly to be the Magus (and low level bards).
Flanking: I was prepared to dislike this, since it's not very 5e of advantage. But on consideration removing spells took out a lot of bonuses so you're not getting swamped in them, and this allow it to work with advantage or disadvantage as well. I'm good with it.
Assassinate: Like it for this sort of game. May I suggest expanding it to the "you have no weapon ready and the enemy has a blade at my throat" as well as stealthily and half CR, that fills a lot of story needs including when foes get the drop on the PCs.
Crits and fumbles: Cutting out casting speeds combat, we can afford this. They usually favor the foes - dead monsters don't take time to heal, they just get replaced.
