For myself, I did briefly play a Paladin/Warlock (can't remember if I was human or half-elf). Instead of the Eyebite/Challenge approach to make it hard for them to hurt anyone, I went with the Hellish Rebuke / Divine Challenge combo - so that no matter what they do, they end up taking damage. I've found that the Eyebite trick, while effective, tends to mainly cause frustration for the DM and slow combats down. Whereas extra damage everywhere is always fun, and helps speed things up!
Yeah, I thought about this for a little bit, but the Hellish Rebuke combo often does less damage than what I am thinking of and also encourages the NPCs to not attack the heavily armored Paladin Warlock.
The Eyebite trick is situationally useful, not something done every round. Using it against Artillery, for example, only works if one can pin the NPC against a wall. It needs to be used when it can be used in conjunction with Opportunity Attacks when possible. So, the PC needs (IMO) a different Warlock power for more significant ranged damage, hence, the PC needs to be Human.
For the more significant damage, a Human Hybrid can put 20 in Cha and use Arcane Reserves at level 1 if not using any Con based Warlock powers and using only Cha Warlock and Paladin powers. Having a Con based non-Human Paladin Warlock typically means 18 Con and 18 Cha. -1 to hit, -1 damage from the 20 Cha build.
So, the Divine Challenge does 4 instead of 5, and Hellish Rebuke does between 2D6+4 and 3D6+8 instead of the D6+D10+7 of Gift of Avernus (which will also hit more often, +1 for 20 Cha and rerolls). If the NPC attacks someone else, that damage will typically be 2d6+4+4 (15 average, 10.85 DPR) hitting 60% of the time as opposed to D6+D10+7 (16 average, 14.5 DPR) hitting 88% of the time (65% with one roll plus 23% with a second roll).
Hellish Rebuke totally incentivizes the NPC and his allies to go attack someone else (taking 4 damage instead of the potential extra D6+6) and since the Paladin armor results in a high AC, the Paladin Warlock will not trigger Hellish Rebuke extra damage every round (especially if the targeted NPC is attacking someone else and his allies do not want to more quickly kill one of their own). It is true that Hellish Rebuke averages more DPR if it triggers, but if the NPCs are played even slightly smart, it won't trigger most rounds.
And to me, incentivizing the NPCs to not attack the heavy armor PC is the opposite of what the PCs should be doing (course, going invisible will sometimes do that as well, but if used mostly when an OA is more or less forced if the foe does, it works out better in the long run). For a normal lightly armored Warlock, Hellish Rebuke is perfect. Go attack someone more heavily armored. For a heavily armored Hybrid, it's questionable.
Granted, I haven't yet decided to go with a 20 Cha, but I'm pretty sure I'm going with a Human for the extra power, feat, and +1 to two additional NADs. If I drop the Eyebite trick, I might go with a Halfling (I really like the flavor of a Halfling in Plate armor) or a Tiefling or even a Dragonborn.
Another possibility is to go with Human 18 Con, 16 Cha, Hellish Rebuke and Gift of Avernus. On rounds that nobody triggered the Hellish Rebuke, fire off Gift of Avernus and if it misses, get the free Hellish Rebuke damage for the previous round's attack.