couple issues.
Helm was the site of their landhold, so they were supposed to be there. their dependents and conventional vehicles were on world, while their mech force was offworld on campaign.
the attackers who hit their landhold on helm were FWL regulars, carrying out orders obstensively as a result of the warcrime the GDL had been accused of and the fact they went AWOL to helm instead of go before a court.
and they didn't find the Helm data until the end of that whole snafu, right before they left helm. at that point they had very little left in the way of hardware.
even if the above wasn't in play, the fact is that victory in such a mission would entail a major derailment of canon setting history, likely resulting in the GDL no longer existing and the entire tech Renaissance being prevented.
good idea, but needs work.