You know you're a tank when unphased by a bump bigger than your head.

They have one other weapon...if they invent the spell card rules, they have Sakuya's time-stop ability. Though I have no idea if she would mention that or not.

The Youkai Tree incident and it's sealing (with Yuyuko's dead body), happened more than 1000 years ago. And The Great Hakurei Barrier were cast around 900-1000 years later. Not to mention, Hakugyokurou was separated from Gensokyo, until the spring snow incident.

Sakuya really messing around with timeline this time.

I hope this hasn't been mentioned already, but... Even without the barrier, couldn't Suika just gather all the ghosts if some got away?

I don't think so. Suika's power seems to be based on materiality, so I doubt that she could gather something without any physical form. But, really, who knows?

Chang chang. 4 Devas have gathered!