Hello,
No. Primitive 'Mech Armor is simply less efficient per ton than modern standard (BAR 10) armor. At the time of its debut, though, Primitive Mech armor was the first technically and economically viable armor type to boast BAR 10 (outside of the armor used on large spacecraft hulls). Lesser technology ratings came to achieve effective BAR 10 protection only by laying it on thick (as demonstrated by their higher weight-per-point rations).
Hopefully, that helps.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs