These things would work fine as you mention... in 10man Normal.
25 heroic though, thats another page, you have more then twise the viles, twise the valks, and sure you have more then twise the members but you can easely spot whos grabbed in a 10man, where only 2 valks exist. But in 25man you have so much people spreaded all over for defile at the same time as valks come down, due to this ALOT of members are on the compleately other side and cant dps the valks (because of the bug on how fast defile grows they have to spread insanely much aswell), you also have 4 valks you need to look at and lets say, 3 people got grabbed out of 4 valks, you have, lets say 4 dps on each, not nearly enough so all 3 people get thrown off.
I would love to raid like you guys too, but for LK 25 heroic, thats just impossible, you might be able to do the soaking with more soaking classes and have them placed right, but that would also mean sacrifising a better raid comp, and a bigger risk of letting LK enrage after frostmourne if someone dies from viles in phase 3 (wich is also a bug), but Valks would still be way to hard.