Despite having a strong anime influence, there are no “giant robots”. By giant robots, I mean those that are 30+ feet tall.
The mecha that do exist are about the size of Landmates (Appleseed), Battlemovers (Bubblegum Crisis) or ATs (Armored Trooper VOTOMS), that is they are no more than 20 feet (6 meters) tall. Depending on the size and design, the pilot may be comfortably ensconced in the torso much like how Tyger was with the Blue Steel Special/Zero.
Angelus’ mecha corps, for the most part, would consist of 2nd or 3rd generation mecha and in fairly small numbers. Despite being behind “the power curve” with technology and low numbers, the mecha that are present are sufficient to defend Angelus from (more or less) mundane threats such as pirates and similar threats. They are much more effective when supporting or being supported by other XSWAT elements.
While the Treaty of 2088 prevents Angelus from maintaining a sizable force or even developing its own mecha, this does not stop certain companies from using Angelus as a testing ground of sorts for new designs. This is where you get things like the Blue Steel Project from Mishima Heavy Industries—XSWAT only gets to keep one or two prototypes during and after the project. It can be assumed that due to the limited cooperation (not many companies are going to do something like this), lack of production (and thus limited numbers) that these things are generally considered exceptions and are thus allowed under the Treaty of 2088.