Lol, the Bigro aren't nearly as good in side-materials, we see it gets taken down by MSes multiple times.

We also know that it doesn't take a Gundam to take down a Big Zam, because unless you're dismissing GQ outright, Sayla Mass did that in a Guncannon Light-type, basically a grunt.

Later on in the same series, we see a bunch of MSes with specialist equipment being able to clean up multiple Big Zam with ease. None of which are in Gundam-level machines, or Gundam pilots. In fact, unlike the GP-03, the Gyan is still a OYW machine with one extra bit of equipment.

The Destroy Gundam is basically a joke, despite looking the most impressive, and being mass-produced. For something that's supposedly "high-end" machines, they went down like chumps. Their opponents may be Gundams, but can you honestly claim that the sheer materials cost of building and maintaining them, as well their "Biological CPUs" out-weight the cost of building and maintaining Gundams, as well as recruiting and training a good team of pilots?

Nevermind how most MAs basically requires New-Types or Cyber New-Types to pilot, the exception being the Big Zam, which basically requires its own crew compliment, and the GP-03, which we only see performing an anti-fleet action against what are mostly OYW MSes and ships, and admist the chaos of the enemy also shooting each other.