Whether via the Help action or the Use an Object action or just ordinary interaction with an object, can an Unseen Servant distract your enemy so as to grant advantage to your attack on that enemy?

The Help action says:

...you can aid a friendly creature in attacking a creature within 5 feet of you. You feint, distract the target, or in some other way team up to make your ally’s attack more effective. If your ally attacks the target before your next turn, the first attack roll is made with advantage. (emphasis mine)

And the Unseen Servant spell says:

Once on each of your turns as a bonus action, you can mentally command the servant to move up to 15 feet and interact with an object. The servant can perform simple tasks that a human servant could do, such as fetching things...

I know that we have an excellent 4e Q&A already on the general topic of Unseen Servant use in combat, that probably applies just as well to 5e, but I think does not address the specific question I have about creating a distraction.

The scenario in question

When a fight broke out in a kitchen, one of my players had his Unseen Servant carry a stack of dishes into close proximity. Then the player said, "The Servant will take the Help action, dropping the dishes to make a distraction."

I said I don't think an Unseen Servant can take the Help action. So the player said "The Servant is still going to shatter those dishes, which by the way are floating in the air right now, which I would think is pretty distracting to begin with."

I ended up ruling that the player would need to Ready his Attack action, then use his Reaction to time the attack with the Unseen Servant's shattering of the dishes; only in this way would the attack come with advantage.

The player begrudgingly accepted this, resenting that I made him delay his Attack until later in the round and use up his Reaction for it.

Did I rule correctly, based on the rules as written?

RAW, I believe that the Unseen Servant cannot take Actions, but can drop plates.

This spell creates an invisible, mindless, shapeless, Medium force that performs simple tasks at your command until the spell ends.

The spell does not say that it's a creature, or other being capable of taking actions. Things do what they say they do; note that the Find Familiar spell says that the summoned thing can take actions.

Your familiar acts independently of you, but it always obeys your commands. In combat, it rolls its own initiative and acts on its own turn. A familiar can't attack, but it can take other actions as normal.

However, the servant is capable of doing simple tasks that a human servant can do:

Once on each of your turns as a bonus action, you can mentally command the servant to move up to 15 feet and interact with an object. The servant can perform simple tasks that a human servant could do, such as fetching things, cleaning, mending, folding clothes, lighting fires, serving food, and pouring wine. Once you give the command, the servant performs the task to the best of its ability until it completes the task, then waits for your next command.

I would argue that dropping dishes is something that servants do, and is essentially instantaneous (no hesitation, because the servant is mindless). This should be able to happen during the bonus action on the player's turn, unless there's a reason otherwise (i.e. the activity takes too long).

Result

Causing a distraction by dropping plates is certainly something that the servant should be able to do on the player's bonus action. However, as the DM you get to decide what happens after that. When I DM, I personally use the Rule of Cool - in this case, I'd probably grant a wisdom save or intelligence check for the creature (at an appropriate DC) on the first set of dishes, and then either ignore future sets, or with advantage. If the player starts running around with stacks of dishes otherwise, remind them that dishes cost gold, and people don't like their dishes being stolen.

I would not allow this

... but you aren't wrong to have done so.

My reasoning is that bonus actions are very tightly restricted compared to actions. Off the top of my head I know of no bonus action that allows another person to get advantage on an attack roll.

Help is specifically an action - that is if you choose to give one ally one attack with advantage then you essentially give up most of everything else you can do on your turn. Allowing this to happen as a bonus action is OP. Allowing it to help you is even more OP.

So the Unseen Servant makes a noise behind the combatant - why should that give advantage? I mean having a raging barbarian bellowing like a bull with an actual great axe behind them doesn't.

According to official 5e rules designer Jeremy Crawford, unseen servant does not count as an ally and therefore the question of whether or not it can use an action to help is moot.

PHB 173:

The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result

So, I would believe that depending on the circumstances Unseen Servant might or might not create enough distraction to grant an advantage on an attack, even if that wouldn't count as a Help action. In your case, I would probably rule in player's favor.

No, because it duplicates an existing specific ability.

Allowing somebody to use Help as a Bonus action from range (30 feet) is a specific ability granted to the Mastermind Rogue via Master of Tactics. It should not be something that any spellcaster who picks Unseen Servant should be allowed to do (and at potentially longer range, 60 feet, to boot).