I have owned 10+ phones during the last 10 years, and the Nexus phones were only ones I bought new.

- Nexus 5 was low cost and amazing for the price. I was able to forgive every issue it had. And another international friend also asked me to buy it & ship it to her.

- The 5X was not low cost, but then it could also be bought cheaply through the Google Fi "loophole." I know at least one other person IRL who bought it through the loophole.

What was that loophole, exactly?

Normally the Nexus 5x was $400, but the cost of buying it through the Project Fi and cancel right away was $250. Now the loophole is with the Moto X4.

Well, none of them have been massive successes so I am not sure it is worth comparing them to Essential.

For long, Google has mostly sold nexuses in order to have demonstration devices of what Android could/should be.

Also, they needed dev devices for their engineers working on the next Android version anyway so it made sense to go the extra mile and sell a couple of them as well.

I don't think any of them has ever been low budget (below 200$); some have been middle budgets and some other high. The Nexus 4 has been introduced at 300$ IIRC but it was not the rule by any length.

Of course, the Nexus 4 cost $299 on launch

Generally, yes.