First of all, I never said she is "one of the hardest hitting SR". I said best, as in "overall performance". But let's overlook that and point out a couple of things you got wrong: first, her NP buff is the normal NP buff, with the usual multiplier. Nothing spectacular, nothing bad.
Second, her steroid is not "kind of bad". If anything it's better than average, going up to 35%, where the normal 3T buff is 30%. Euryale's is an example...
Now, you are completely discarding survivability, which is relevant in tough content and an area where she outmatches both of your picks by far.
Her 3rd skill is actually her bread and butter, making her a great tank that can dish out consistent damage with both cards and NP, thanks to her very high atk stat (the highest among 4 star Archers) and her (ironically) above average steroid. While also having good NP gain. Oh and her skill have all good uptime, with a CD of 5T across the board. On top of the rest of the utilities she offers (ignore evasion, which Euryale doesn't have, ignore defense, which both Euryale and Robin don't have, and yes, buff block, which is quite useful in boss fights).
You are also completely discarding the fact that Euryale is relevant in like 1/3 of the boss fights, cause if you don't face a male (far lower in number compared to female) her NP is trash and one of her skills is useless.
Same goes for Robin, if the enemy has debuff immunity (quite common), but he's definitely in a better spot than Euryale.
