I understand the check on absolute power. It is very useful for jobs on GM team and Supreme Court. They have authority and sometimes can't be easily removed. An argument of not trusting someone can be enough for those jobs.
For a Cabinet position there can be supervision by the White House. I don't know how White House operates, if the SoS does its own thing or needs to ask President before making big decisions. If the SOS gets out of control and does harmful things or against the President wishes it can be fired quickly. The danger if you not fully trust the nominee isn't as big.
I guess I was surprised from where the opposition comes from. I would more expect senators from enemy parties opposing the President's nomination. Maybe I am wrong but opposition comes from people that I would imagine are supporting the President. They are stopping the President from staffing the cabinet with people he chose by opposing his pick.
As a detailed analysis of the recent election shows, there was a clear split among left-leaning voters between the Tim ticket and the Sirius ticket, and the Tim ticket only won in the end because of the right utterly abandoning the OSR ticket. Many on the left did not vote for this administration and thus have no inherent reason to trust it.
While there is some oversight from the President, NSC, and GM Team the SOS does not legally have to get permission ahead of time to post orders. Given Laki's behavior over the years, particularly being liable to change positions at a moment's notice, it is hard to trust how he would act in maintaining key relationships with allies across the globe or in handling time-sensitive matters. This isn't personal, and I even agree with Laki's side of the story on things from time to time, most prominently the collapse of the coalition that elected the Tack Administration, it's just simply a recognition that the position of SOS needs someone with a level head whose integrity is beyond reproach. That simply isn't Laki.
Deference to the executive is important, and I've shown it in the past, like in voting for Sestak's Supreme Court confirmation and for Dule as Deputy AG, both cases where I could have made an excuse to vote No but ultimately voted in favor. But it's not absolute. Where a nominee is firmly inept for the job, it's the Senate's role to deny the confirmation, not to "hope for the best" and confirm anyways because "oh the president can just fire them later" and then wonder why there is suddenly a poor response to an emergency situation that becomes an unnecessary headache for all involved.
