I must say, I haven't flown against Fenn Rau much at all yet in general, and have zero games against him with TIEs, but I have had decent success against Soontir in the past, so I can't imagine Rau is invulnerable, especially without Palp or an evade token. Most of what I fly against are 2 ship lists, mostly with low agility. Miranda absolutely melts against concentrated fire, and Bossk doesn't last long either. Dengar and Rey are harder to pin down, but splitting your approach and blocking will leave both ships hurting.
I fly TIEs all the time, but I actually haven't flown Howlrunner in ages. For me, the R1 bubble just puts too much constraints on my flying, and I have to have a split deployment to reliably get 3-4 turns of blocking on the first engagement. That's why I prefer Youngster, Swarm Leader, and Wampa, and snap shot as the upgrades for my swarm. They are all more flexible with movement, which is where the strength of the list really comes from.