Gloriana was delusional if she thought that they could design a standard mech that could fight against expert mechs in a cost-effective manner.
How many mech designers attempted such a feat?
While there were instances where large amounts of regular mechs managed to overcome expert mechs, the circumstances were always special.
First, the attacking side had to bring a lot of mechs. These mechs also had to be fairly good. They needed to be tough enough to slow down the expert mech's attempts at taking them down. They also had to possess enough firepower to wear down the expert mech's defenses.
Even with these conditions, the expert pilot could always decide to run away. It was very hard to hinder an expert mech's flight. Even the slower mech types such as defensive knights always exhibited above-average mobility due to the immense amount of investment poured into their development.
At the level of expert pilots, mobility was an essential life-saver!