1. The pot was hot.
>>> was = linking verb; hot = adj., subject complement.

2. The watched pot never boils.
>>> watched = past participle as adj.

3. The pot was watched.
>>> was watched = passive voice verb phrase.

My question: Couldn’t I just as easily (and sensibly) understand the sentence in #3 as a linking verb (was) + an adjective (watched)? After all, that is how was is used in sentence #1, and how watched is used in sentence #2.

“Being watched” isn’t an action taken by the pot—it’s more of a descriptor of the pot, isn’t it? It’s the watched pot, the pot that is watched.

I watched the pot.

I made the pot a watched pot.

When we use the passive voice, aren’t we essentially turning an action (verb) into a description (adjective)? Making the action a passive state of being?

What’s the value in considering passive voice construction as a verb phrase instead of as a linking verb + past participle-as-adjective?

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Second, where is the line between when (to be + past participle) is considered the passive voice and when it’s considered a linking verb + adjective?

4. That pot was tarnished before I polished it.
>>> unless I’m mistaken, “was” would be considered a linking verb here, and “tarnished” would be considered an adjective… but why? The clause has the same construction as the sentence in #3; why isn’t “was tarnished” also passive voice?

The distinction seems fairly arbitrary… what’s the reason for/the value in the distinction?