Not if you can get access twice. A variety of "evil maid" style attacks exist. For example, imagine I replace your FDE's bootloader with a version that appear

Not if you can get access twice. A variety of "evil maid" style attacks exist. For example, imagine I replace your FDE's bootloader with a version that appears identical, except it also logs your passphrase. Then I come back, read the passphrase, decrypt, and win. For scarier thoughts, imagine I know how to control the Intel Management Engine, and attack that instead. That's not covered by FDE.