FrogReaver
As long as i get to be the frog
In my experience, they serve different functions. I'll do all the rigorous stuff for you, since you're obviously not interested in putting too much thought into this. First, your Orc scenario. Four Orcs, and you Dissonant Whispers one. What happens?
Well, you have 65% chance of success, assuming the Bard's Spell Save DC is 14 and your using the standard CR 1/2 Orc Stat Block. So 65% of the time, you will deal 3d6 damage and Fear said singular Orc. 35% of the time you deal half that damage and that's it. The average damage of 3d6 is 10.5 and the average damage of 3d6/2 is 5(yeah, dice math is weird). You can find the average damage that you can expect from casting this spell by using a very simple equation.
(10.5*0.65) + (5*0.35) = 8.575 and a 65% Fear chance.
Faerie Fire is slightly less likely to hit each individual Orc, as they have +1 to Dex Saves vs their +0 to Wis Saves, which is what Dissonant Whispers targets. So, Faerie Fire has a 60% chance to affect each target and a 40% chance to not affect each target. Iterative probability, yada, yada.
1-(0.4^4) = 0.9744 or a 97.44% chance to grant advantage on at least one target. An 82.08% chance of hitting two. A 47.52% chance of hitting three. And a 12.96% chance to hit all four.
Orcs have 13 AC and our non-casters have +6 to Hit (for simplicity, I'm assuming everyone has 18 in their primary attacking stat. Same goes for all my Bard calculations). This means advantage will increase the average DPR of every non-spellcaster in the party by ~25% and a flat +21% chance To Hit (the extra 4% to Damage vs. Hit Chance comes from the potential to crit. Most Parties have 2-3 non-casters, but let's assume 2 just to be fair. Let's go with a Level 2 Fighter w/ a Greatsword and a Warlock using Eldritch Blast + Hex.
They deal 8.05 + 9.38 = 17.43 total DPR.
17.48 * 0.25 = a 4.37 increase to the party's damage per round. If the Faerie Fire stays in play for 2 rounds, it will have contributed a bit more damage than Dissonant Whispers - the 65% chance to Fear. After three rounds, it will have contributed significantly more to damage than Dissonant Whispers would have. Now imagine if you have three Attack Roll-based classes in your party, some of whom, like Moon Druid or Battlemaster, can CC on a successful hit. And your Rogue will love you.
Which is kinda the hidden, true majesty of Faerie Fire. Your party will appreciate you for it, because it makes them do things better.
And as someone else mentioned, one targets Dex and the other targets Wis. One is a single target damage and CC. The other is an indirect AoE Buff/Debuff. Go play a Bard, take both spells, and see what I mean. Theorycrafting in these super limited scenarios will only take you so far. And I have no idea why you think you can generalize the entire experience of playing Tier 1 with this four Orc scenario. And, I've tried to hold back from asking this, cause I feel it's rude, but I have no idea if you have ever played any of the classes your talking about, or even if you've played 5e at all. (I'll believe you if you tell me you have. I just want to make sure we're on the same page in, at the very least, that regard.)
I hate math.
EDIT: Also, for those of you who are confused by the seemingly hyperbolic exasperation, there's some baggage from another thread here.
Convenient of you to ignore even a single OA for the DW user.