They should just remove the "rapid" from the spell name because unless you're lucky you're not going to have a rapid wall removal, or better change the whole spell name into a variant of "fragmentation" because it progressively fragment the wall, throwing shrapnel to the close monsters and after several tries it finally destroy it.
Managed to defeat every of the Vault:8 stair guardians, not an easy battle as usual, as those guardians had support from several stone giants, a few yaktaur and even a shadow dragon.
So it was obvious that just blinking away and staying to fight on Vault:8 would be plain suicide, though ranged attackers around + the heavy hitters from the stair guardians.
My tactic was to surround myself with imps (wasted 2 acquirement scroll but finally got a book with this) and the zombies i animated from Vault:7 , go down, then immediately go up and hope that Crawl would not have pulled huge damage from just getting down/up with a few monster following.
Then once back upstair, blink away, poison cloud (i have not found any poison resistance yet, so i can't even use it while i'm close) and help my zombies and imps to deal with the guardians with mystic blast.
Worked nicely, though the yaktaur arrows and stone giants rocks nearly killed me in one of the up/down stunt.
But the guardians once killed makes very good zombie helpers.
screenshot of the Vault:7 stair i used for my attack, after having finished the stair guardians of Vault:8 :
Really a pity you can't get the guardians zombies with you, i would really have a need of strong meat shield if i want to survive Vault:8 and with the complete lack of summon book from everywhere i explored, i can't even count on Shadow Creature that would be a very powerfull spell to have in Vault:8
Edit : forgot to put this screen of the stairs of Vault:8, it's a mess there too, an incredible amount of yaktaur has been moving there from every direction.
It was a battle of attrition to get them down, it took so much time that i even had to get back to my Lair stash to refill my food stock.
I explored a bit Vault:8 , surprisingly cleared 2 of the 4 vaults (unfortunately the rune was not in those), got an army of zombies+imps, lost them all in difficult battle.
But more importantly i lost a level due to the several elf draining spells and a few shadow dragon around (having only 1 ring of life protection does not help much unfortunately), only recovered this level by cleaning the 2 vaults.
So always be carefull of draining monsters if you don't have full life protection.