> Theory dictates that with stronger magnets, the reactor can be scaled down (with the square/cube, can't remember exactly), and thus cost and time to develop

Here's the quick summary:

B: magnetic field strength

R: length scale

Fusion rate ∝ (plasma pressure)^2 ∝ B^4

Energy gain (Q) ∝ R^1.3 B^3

Power density ∝ R B^4

Cost ∝ R^3

So, say for example you're targeting a fixed Q. Doubling the magnetic field strength results in R1 = R0 / 2^(3/1.3) = 0.2 R0. And 0.2 R0 translates to 1/(0.2)^3 = 0.008 = 0.8% the cost.

The scaling is absolutely insane, and a stronger magnetic field has other advantages (such as making plasma instability far less of a concern), though structural loads can be an issue (that, at least is a relatively straightforward engineering problem).

If you take 12T for ITER and 20T for SPARC, that's not actually 2x, it's 1.67, which translates to 30% the size and 3% the cost (and time). It should also be noted that this is just rough, order-of magnitude estimation, but it should be broadly accurate.

For a more detailed explanation: https://youtu.be/KkpqA8yG9T4