A question for experienced growers.

[Rusty Trichome]

...or my bagseed was some really good stuff.

Perhaps the grower of your "bagseed" took pride in their work, but was careless enough to have seeds, lol.

Is it possible to have Bud-A that has fewer 'crystals' than Bud-B, but Bud-A is still more potent than Bud-B?

Pore spacing is genetic, but trichomes on a lower bud will mature slower than those closer to the lights.

Does the amount of 'crystals' directly relate to the potency of the bud??

No.

Most of the time, do sativa dominant strains have less 'crystals' than indica dominant strains?

Depends on the strains, but trichomes are tricky, and visually can't be relied-upon to be an accurate gauge of potency. (maturity, yes...potency, no)
I've smoked strains that were really tasty, with shitloads of trichomes, but didn't get you high. I've also smoked some male leaf that would make your eyes bleed.
Also depends on what type of effect you're looking for. Trichomes that are just turning milky (almost mature) have a bit different effect than mostly milky, with some rusty trichomes showing. (getting very mature)