And why isn't someone who has been writing the legislation that the country will be following in the event of a catastrophic crisis not the person to choose to execute those very laws? Why isn't someone who is charged with declaring war in the first place capable of discharging those war powers?

If you're going to quibble with the succession, then you had better start working toward a Constitutional Amendment because the Constitution says that Congress is the one who shall make the law about how succession works:

Article II, Section 1:

Congress may by Law provide for the Case of Removal, Death, Resignation or Inability, both of the President and Vice President, declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed, or a President shall be elected.

The law in 1792 had the President pro tempore of the Senate being next in line followed by the Speaker. This was changed in 1886 to go through the Cabinet, making the same argument you are making now: None of the Congress would have had executive experience.

The law was changed yet again in 1947 to what we have today: Speaker of the House first, Preside pro tempore of the Senate, then Secretary of State, then Secretary of Treasury, then Secretary of Defense.

To say that Speaker is not involved in the ongoings of the administration is to deny reality. Who do you think the administration works with to pass legislation? Since Congress is the one charged with defining the law, why on earth do you think they are incapable of administering it?

Let's go with your "we're under attack!" paroxysm. Do you really want the Secretary of Defense to leave his post to take over the rest of the functioning of government? Shouldn't he stay where he is needed and isntead we install someone who is familiar with all aspects of the government because they've been writing the laws that define the government?