Light Cavalry
Pairing the soaring Valkyrie Redeemer with a submachine gun granted the mech sufficient ranged firepower against opponents at medium range.
Submachine guns, which were light enough to be wielded by a single mech arm if necessary, weren't known for their accuracy.
Even though there was a lot of overlap these days, the mech industry still maintained a conscious distinction between various ranged weapon types.
In general, rifles were quite effective at different ranges. They worked best at medium range but did not become useless at longer or shorter ranges.
Submachine guns didn't have to cover so much ground. In exchange for increasing their firing rate and decreasing the burden onto the mech, this class of weapons straightforwardly sacrificed long-ranged firepower in favor of increasing their effectiveness at shorter ranges.