I have something to say:
Taken from the SWTOR Encyclopedia, published in 2012:
"But perhaps the most famous aspect of Mandalorian armor is its resistance to lightsabers, thanks to the special properties of the unique iron used in the armor's construction. Known as Beskar in their native language...."
So do Mandalorians get Beskar? Well, the newest source for SWTOR says so. If SWTOR mandos had it, obviously Mandalore the Ultimate had it as well.
"....this metal is exceptionally durable for its weight, though only a select few Mandalorian craftsmen know how to to work the metal to maximum efficiency."
It stands to reason that these advanced armor makers died out by the later years (AKA: The Clone Wars) and that is why we see the difference.
EDIT: However, as seen from the Usage section of this Wookeepedia article
, it was only used in full suits very rarely. Usually, it was employed in gloves or smaller pieces of armor that are used less.
So not every Mandalorian would have Beskar Armor.
I also cannot find proof that Neo-crusaders used Beskar at all.
What does this mean?
1. Certain Mandos might have an occasional defensive advantage
2. Mandalore (who we assume has full Beskar) can face Grevious and not auto-lose
And just so y'all know, I'm siding with Grievous on this one. Just wanted to even the playing feild for Mandalore.