Question: Why don't the heroes use at least 2018-era protective gear to keep from getting shot or stabbed?
Question: Not sure if there's an answer, just speculation, or a plot hole. As I understand it, the premise of time travel in the show is the Legends can't go back to a time they've already been to because then time would fold in on itself, etc. For example, the 3 get stranded in 1958, picked up in 1960, but the rest of the Legends can't try again by just going back to 1958. But then it's revealed that Chronos was Rory all along, so how is Chronos/Rory able to time travel back to a time Rory has already been to without doing any real damage to time? And if the idea is, well no-one knew Chronos was Rory, so they didn't know they were interacting with a time traveling version of themselves (or what ever the reason), then all the Legends have to do is disguise themselves to interact in the same time.
Answer: My speculation... As Chronos was sent by the Time Masters, the armour he is given may have some sort of 'time folding preventive' system built into it? (A pure assumption on my part).