Kim Thayil is good but Mike McCready makes him look an amateur. One can look beyond Pearl Jam and what he did with Mad Season (a group featuring Layne Staley amongst others). There is an instrumental on that album called "November Hotel" where he goes off something shocking.
Matt Cameron has being in both groups although I think Soundgarden allowed him to show off his wares better. Another factor is that although Cornell in his prime was a vocal god, he is now a shadow of his former shelf whilst Vedder arguably is a better vocalist now...at least no worse than 92.