I don't think there is a good synergy between those features.
As you wrote:
And as Whirlwind Attack is written:
"You can use your action to make melee attacks against any number of creatures within 5 feet of you, with a separate attack roll for each target."
You make more than one melee...
My favorite crit-fishing build:
Point buy:
STR 14
DEX 10
CON 13
INT 8
WIS 12
CHA 15
Race: Half-elf (drow variant to darkness and fiery fire) / +1 STR and CON / + 2 CHA
Classes:
Fighter level 1 - Saving throws, heavy armor and Fighting style
Hexblade Warlock 5 levels - Pact of the blade, extra...