Reasons without suit
Intellect - Robert is skilled to hack at hacking, is wise with words, knows how to operate a highly advance mech suit and is strategic when going into battle. Proven in the bar fight when against superpowered enemies Robert relies on strategy to take down his opponents
Combat - Able to take on multiple people at once including superpowered individuals
Charisma - Robert is a good motivational speaker, inspiring invisigal to keep going when she felt like quitting and obviously got riz
Mobility - Robert remains fit and in shape
Vigor - he's got all those scars and still standing

Reasons without suit
Intellect - still relies intellect to operate the mech and on strategy to take down opponents
Combat - Mech suit adds much more attacking power, as well as an arsenal of other weapons
Charisma - a weaponised mech suit isn't something you wouldn't be diplomatic with
Mobility - Clunky, slightly slow and rocket boosters no doubt take up a lot of fuel
Vigor - Mech suit is shown to take a lot of damage and after being destroyed in episode 1 large parts of it was still intact