That is a very fair criticism!
There are several things to address this that wasn't added in time, such as roguelike-upgrades that favor only several modes, making Gun / Movement eliminations more valuable.
As of the submission of the jam, the only disadvantage of choosing Frail / Ordinary is a (invisible) lower score multiplier of 0.8x as opposed to the other's 1.2x score multiplier, so you'd be right in your assessment to believe that that is the best way to survive the longest, ignoring the scores. I wanted to put EXP modifiers as well (Picking frail goblins will give you lower EXP, so you can get outscaled rather quickly), but decided against it last second as there wasn't time to playtest the values, and people weren't picking up on "more kills = more levels" to keep up with the goblins' strength and just run around anyways.
Thank you for playing!