The unitary executive approach is pretty extreme. In one recent opinion before they pulled the trigger, Roberts court admitted that they could have reigned in the excesses that followed Humphrey's Executor, implicitly admitting its fundamental reasoning was well grounded. That was quite an admission because Roberts had been championing the unitary executive since the 80s.

In fact, few legal scholars dispute that the executive power is unitary, though they might disagree on the implications. As Humphrey's explained in detail, the issue is about areas of the government where the executive nominally overseas work that has a congressional or judicial character. For example, administrative judges and Federal prosecutors exercise a kind of judicial power. And the whole Federal Reserve exception SCOTUS quickly formally carved out is because the Fed exercises a kind of congressional budgetary power.

Humphrey's said that when an agency or officer is exercising a non-executive power, Congress can limit the president's control over how it can be exercised, including reasonable limits on the president's ability to fire the officer.

Ignoring unitary executive proponents like Thomas who choose to ignore the ambiguous intentions of the constitutional drafters, or the early history of the first congresses actually limiting some executive power over officers, people like Roberts primarily argue that Humphrey emphasis on the character of the power is just too difficult for the courts to police; they want a brightline distinction defined by whether the office is nominally under the executive branch, even though that approach is in tension with the actual, if equivocal, original meaning of the constitution. But not too brightline, because letting the president control the Fed was a bridge too far. So they created that exception which clearly is rooted in the same logic as Humphrey's, but they (ironically) pretend it's just something they pulled out of thin air as a one-off.