I doubt Kyuss should be on the list, and since they never had a charting album in the US, if they did make it, it wouldn't be for being big.
Id say both soundgarden and alice in chains would be equal to the peppers and pumpkins in impact and influence and lose out on popularity .... Chains were overall more popular than SG, SG had 1 big selling album , but Chains had Dirt which is about equal and several multi platinum albums , SG and Chains are about the same in impact, heck , Chains had the 1st grunge album in the top 50, and Man in the Box was huge before Nirvana came on , so I disagree big time there, and theyd tie influence .... so Chains rightfully are above SG , dont know about the positions on the list ..... when i see people like Mariah Carey and 2 Pac and Chains on the same list, i cant think straight ....
Superunknown went 5x platinum; Dirt went 4x platinum. Soundgarden had 1 other multiplatinum album, Badmotorfinger, and Alice in Chains had 2 others, 3 if you count Jar of Flies. But Soundgarden is probably bigger than AiC in the UK. AiC probably takes popularity, but not by much.
First grunge album in the top 50 would be secondary influence if it's anything. It wouldn't count for very much, because most of the subsequent grunge and post-grunge followed either Nirvana's or Pearl Jam's model of grunge rather than Alice in Chains', and because first grunge album in the top 50 is a small degree of popularization when it had previously charted and became much more popular later.