Very informative, I think this will be K-Canon in our approach to Mandalorian iron. And there is actually proof that Neo-Crusaders used Beskar. See here. In physical and technical specifications it lists structure as Mandalorian Iron. The source of this is most likely an anonymous Neo-Crusader from KOTOR or KOTOR 2 boasting about his beskar, I seem to recall that. So we can assume that Neo-Crusader armour was reinforced with beskar at least.
Apparently, according to Wookieepedia, the neo-crusader armor had a "harder surface" than the normal crusaders. So we can assume that the bulk of the mandalorian (neo-crusader) armor was not actually Beskar, but another metal.
HOWEVER: The reason Beskar matters here is because Mandalore undoubtedly has a full set. And that makes him hard to kill.
B1 battle droids kinda suck. But Super Battle Droids, Magnaguards, Commando droids and Droidekas rule
The CIS were strong enough to challenge the Republic, however they were pretty much on the back foot for most of the Clone Wars which lasted only 3 years. But the Republic had the best defenses of any Republic era, the Grand Army of the Republic, as well as a formidable Republic navy.
The Mandalorians were also strong enough to challenge the Republic and in the first stages of the war where far more successful than the CIS ever were in the swift conquest of the Outer Rim. However once the Revanchists got involved, which was not even the full Force on the Jedi Order, they began to lose. However the Mandalorians managed to hold their own against the Republic for 16 years. However the Republic Navy and Army was not as effective as it was during the Clone Wars.
Just something to consider.
Saying that the Mandalorians were more swift in their conquering of the outer rim doesn't make any sense. Planets joined the CIS instantly once they declared independence. Also, this map
shows that they controlled a good chunk of the galaxy, as you said, in under three years.
Saying that the Mandalorians held out for 16 years isn't exactly fair, considering the CIS lost instantly when their leaders were killed by Darth Vader. We have no idea how long they would have gone on.