That is not entirely correct. Certain Flashpoints do have reactions going on if you're soloing it. In Maelstrom Prison, if you make it to Kilran all by yourself, he will comment on it, saying something along the lines of it stretching credulity that a single operative caused all that trouble in the Maelstrom Prison. Likewise, in False Emperor, if you have HK-51 with you and you win the role for "Hello, HK-47", HK-51 will make a snarky remark about how outdated HK-47 is. That even happened to me when I was in a group of four and HK-51 was merely the companion I had on standby.
Wait so I can have HK-51 on standby and get that? I really need to try this then.