That's pretty standard point of balance, an 3-dot artifact is roughly equivalent to an essence 3 solar charm or terrestrial circle spell. It's not
quite as equal at Essence 5 Solar = Solar Circle Sorcery = Artifact 5 though.
Anchors are basically Backgrounds you have to hold onto and channel your sorcererous power through- you can't just pay motes and cast spells anymore. The idea is that ES wants to encourage Sorcerers to act in a sorcerer-like way by connecting their powers to concrete things that can be engaged with or invoked.
According to ES's model, with some exceptions, when you invoke an Anchor, you are committing it for the duration of the spell's effect. This is is to encourage you to cultivate hoards of backgrounds and use them as spell-charges. To keep things relatively sane, he limits anchors along thematic or potency lines. This is why under his model Resources can't be used as an Anchor as it's not 'potent' enough, but 'my authority as king (backing/followers' can, because the sorcerer is channeling the power through his Background.
In the case of the Followers/Backing channel, the idea is that while the spell is working/being cast, the 'background' is committed and can't be used. In-practice, Followers don't magically dissappear and the kingdom does not cease to exist. Instead those backgroudns can't be used for any other meaningful dramatic-scale action. You can still TALK to your followers, but you can't order them to build a dam- that's what you're using Sorcery for.
Now, ES specifically wants it so that you buy a spell wtih a specific anchor in mind, not a class of anchor. In Inks's case, she can
only cast Invulnerable Skin of Bronze through her bronze-skinned tiger-familiar. It was that or her daiklave, and I basically told Aleph "As presented, I can either have defensive magic but no weapon, or a weapon and no defensive magic'. I can accept needing more backgrounds to incentivize sorcerer behavior, but there's a fair amount of Exclusivity involved.
On that note,
@EarthScorpion I think what might help Anchors is if you approach them as more of a carrot than they currently are. As I mentioned previously, they as much feel like the hearthstone tax-but-not-as-bad. What might work better is if Anchors were presented as bonuses you seek out to make your spells better in some way. Sure you can cast
without an anchor, but you're rewarded for doing so with one. Some exceptions can still
require an anchor like the demon summoning and so on.