I was just discussing this word with a native speaker. His preferred definition (for which he showed me a source) is "fighting hard". He says がむしゃら mostly has a positive nuance. But in Renshuu's dictionary and also in Jisho.org, がむしゃら is defined as "reckless; daredevil; frantic; foolhardy" which seems to be slightly inaccurate and also carries more of a negative nuance.
I think frantic covers a lot of territory, including things like fighting hard, without necessarily being negative. So you’re really just debating the nuances of which definition should come first.
The article below, seems to indicate that 我武者羅 means "doing something with *reckless* abandon". Similar to 猪突猛進
Which certainly can have a negative nuance to it. That's the definition, that I'm familiar with.
But, the article also seems to indicates that over time 我武者羅 has come to mean "working hard", (without the negative nuance) and that this usage tends to be the more prevalent one now.
