Rapid Shot AB penalty can be eventually removed with a Mythic Feat. Soheis can even stack Flurry, Rapid Shot, Manyshot and Mythic Manyshot. Less damage per shot, but much better Accuracy with Weapon Training.
And well, please don't use Perfect Strike in those discussions. This ability is rather terrible, outside of Vital Strike builds maybe. It affects only the first shot in the full attack (out of 7 or so), so its very sad next to Touch of Luck, Fortune Hex or Brilliant Inspiration.
If you need it to hit a boss, you're in serious trouble. And a single crit won't kill many bosses.
(1) Mythic Feats are the most valuable (and scarcest) resource in the game. Not needing to burn one is a significant advantage. If you forgo Snap Shot line you can skip Rapid altogether.
(2) Lann isn't a Sohei and Sohei is bugged but ranged Sohei needs the help so Owlcat isn't fixing it. Sohei Weapon Training doesn't advance.
(3) Point being is Lann starts with *twice* the attacks of anyone else with no penalty.
(4) On Perfect Strike you're comparing apples to oranges. It's only the first attack on TB. One of the many hidden advantages of RTwP. And it's a Free Action unlike the others, which doesn't require another character to burn their whole turn.
Let's look at the math:
Keen Longbow with Bless Weapon.
Chance of autocrit in one Full Attack using Perfect Strike with four attack (say for Nulk fight) = 1 - .9 ^ 8 = 57%, at seven attacks (if you can get it activated) that goes to 1 - .9 ^ 14 = 87%
(5) Whether you need it to hit a boss depends on where you are in the game. There's no shame in using it until you get the items and abilities to hit them naturally, and it prevents key crit misses as well. Usually.
Here's some illustrations. You can tell by the font that some of these go back to alpha so I hadn't figured out all the ways to max damage, but even then the value compared to other toons was evident.
Attacking Minagho turns out to not be the best idea on this fight, but you can see that Perfect Strike makes Deadly Aim a more viable option and he has plenty of Perfect Strike activations for this whole fight. Also not the first attack.
Playing pretty badly on Core saved by Perfect Strike. Notice the spell interrupted. That's probably my main use for it.
Two more examples of using Perfect Strike to make sure an interrupting shot lands.
Damage is halved because Ghost (and still pretty crappy) but Lann still saves my bacon in a helluva fight.
Seven attack example but first one gets there. Not enough to outright kill but enough to finish off with next attack even without crit.
Perfect Strike not even activated on this one but this amount of damage is relevant with Cleaving Shot even if it doesn't outright kill the boss.
Didn't get it activated in time on this one either but again goes to OP's point that ZA Lann does hit hard.