PVP comparisons are always bad to make. It reflects a small portion of the community, and a minuscule part of TOS’s content, and that’s before the PVP balance patch making it further irrelevant.
Murmillo’s have extremely high modifiers, and while they do have lower base damage if they use a one-handed Sword, or even the same damage if they are using a one-handed spear, their class sacrifices nothing for the additional defence of a shield. Shields certainly do help with survivability, especially in a class that encourages the use of Peltasta, and with utilising their helmet. Murmillo’s have utility in the forms of Peltasta, which again they sacrifice nothing to use it compared to a Dragoon opting for it, and they have their own set of debuffs. Murmillo’s have the same damage, with a fair amount of utility, all while having a large increase in survivability they lose nothing to obtain.
Doppel’s are interesting because they do end up sacrificng much of their own survivability, but their damage is insane and easy to use, which does make it more questionable like I said. But again, making PVP comparisons is unhelpful, especially since you brought up Cata-Goons while Hop-Goons also exist which makes much of the Dragoon population suffer from the same problems.