The Dragon! The Dragon! the Drag- what, no not the 'mech the, ah whatever.
While i haven't personally gotten to field any protomechs (can't bring myself to sneak them in demonstrations, which is all i've played in ages) i can respect the concept, and it's hard for me to argue with the stats the Delphyne has.
i also like choice to give them flashy looks, for what it's worth. they're right in that sweet spot of "what IS that" with their size, speed, and the claimed fluidity of their movement that you can drill some real panic into infantry and civvies with them, and people afraid of you tend to toe the line which is dandy work for if you're taking a planet. sure they could have just skipped it, but then they'd just be small 'mechs and not nearly as terrifying.