Learn Hardcore Japanese: netto de genin wo sirabeta ga, tyokusetu kiita hou ga hayakatta. - I looked up the cause on the internet, but asking directly was faster.

Because the fixed pattern is V-たほうが + (adjective/いい) to express preference or hindsight (“would be/would have been better/faster”). It does not literally mean the action happened.

General rule: ネットで調べるより、直接聞くほうが早い (neutral, general truth).
Hindsight about a specific case: …直接聞いたほうが早かった (“It would have been quicker to ask directly.”).

Does 聞いた here mean they actually asked, or that it would have been faster if they had asked?

In this construction it typically means the latter: “It would have been faster to ask (but I didn’t).” If you want to say you actually did ask and found it quicker, say something like:

結局、直接聞くのが一番早かった。
直接聞いたら早かった。

Why is が used between the clauses? Could I use けど?

Here が is a conjunctive “but/though,” not the subject marker. It’s slightly more formal/written than けど.

Casual: …調べたけど、…
More formal: …調べたが、…
Stronger “even though/contrary to expectation”: …調べたのに、…

Why is で used after ネット? Could I use に, を, or から?

で marks the place/means of the action: “to look it up on/using the internet.”

に is for location of existence/arrival, so not natural here.
を is an object marker, not correct here.
To say “from the internet,” use から: ネットから情報を得た.

What does 直接 modify, and do I need に (直接に)?

直接 is an adverb modifying 聞いた. In modern Japanese, 直接 is used without に by default. 直接に is possible but sounds stiff/old-fashioned. Synonym: じかに.

Does 聞く mean “ask” or “listen” here? How do I show whom I’m asking?

Context makes it “ask” (contrasted with searching online). To indicate the person, use 人に:

先生に直接聞いたほうが早かった。 (“It would’ve been quicker to ask the teacher directly.”)

Why is 早かった in the past? Could I use 早い?

Past tense evaluates a specific case in hindsight. …早かった = “was/would have been quicker (in that situation).”
Use 早い for general truths: 直接聞くほうが早い.

Should it be 早い or 速い?

早い = early/sooner (time).
速い = fast/rapid (speed).
Here you mean “sooner/quicker to get an answer,” so 早かった is natural.

Why is 方 written as ほう?

In the set pattern ほうが, many writers prefer hiragana because it functions grammatically as “the preferable side.” 方 is also acceptable in ordinary writing: 聞いた方が.

Why is there no の before ほう (i.e., why not 聞いたのほう)?

When a verb phrase modifies ほう in this pattern, you don’t insert の: V-たほう, V-るほう. のほう appears when a noun (or a noun phrase) precedes it: AよりBのほうが….

Can I reorder to 原因をネットで調べた? Any nuance difference?

Yes, both are fine:

ネットで原因を調べた (method/medium first).
原因をネットで調べた (slightly highlights the cause).
No major change in meaning.

Do I need the comma after が?

Not strictly. A comma after conjunctive が is common and aids readability, but …調べたが、… and …調べたが… are both acceptable.

How do I make the comparison explicit with “than looking it up online”?

Use より:

Specific/hindsight: ネットで調べるより、直接聞いたほうが早かった。
General truth: ネットで調べるより、直接聞くほうが早い。

If I actually did both and found asking was faster, what’s a clear way to say it?

Avoid the hindsight pattern and say:

ネットで原因を調べたが、直接聞いたら早かった。
結局、直接聞くのが一番早かった。

Why 原因 and not 理由?

原因 = objective cause (what produced the result).
理由 = reason/motive/explanation (often subjective).
When diagnosing a problem, 原因 is the natural choice.

Does 直接 imply face-to-face, or could it be phone/chat?

It means “without an intermediary.” It can be face-to-face, a phone call, or a direct message—so long as you ask the source directly.

What would a more polite version look like?

For polite speech:

ネットで原因を調べましたが、直接伺ったほうが早かったです。
You can also use お聞きする: 直接お聞きしたほうが早かったです。
Use 伺う/お聞きする when being polite to the person you’d ask.

Could I use のに instead of が?

Yes, to add a stronger “even though” nuance:

ネットで原因を調べたのに、直接聞いたほうが早かった。
This implies frustration/surprise that, despite researching online, asking directly (would have) turned out quicker.