When was Roman army at the height of its power?

[Mrbsct]

And how does that weaken the army of the 2nd century? If anything poor preformance of the army was not reported till the mid-4th century by Zozimus and Vegetius.

The Emperors of the 2nd and 3rd centuries were much more warlike and less forgiving. Augustus if anything did not prefer expansion, stopping his expansion on the Rhine and ending the war with Parthia. The 1st century army got mauled multiple times, in Germania and in Parthia. Emperor Nero didn't even bother fighting the Parthians.