Is the Arena default deck "Line of Fire" bad or is it just me?
The default decks are all bad. Just look at the cards it runs - it has underpowered spells like Infuriate, underpowered creatures like Slaughter-Priest of Mogis, and doesn't max out on the actual power cards like Kroxa.
Of course, the point of the default decks is to give new players a taste of Magic's gameplay. From that point of view, the fact that good decks will destroy this one isn't actually a bad thing, and chances are it was constructed to provide an enjoyable game against other default decks. It is entirely possible this deck is bad relative to other default decks - I have not played or followed Standard for several months so I do not know - but that would just be a sign that you should upgrade this one by replacing the bad cards with good ones (hint hint).
What this means is ...

If you are looking to play a fair game (i.e. both players have similarly-powered decks), try the draft formats. Caveat: last I saw these formats are expensive to enter, and quite skill-intensive. As a new player you could very well lose gold quickly.
Alternatively, you can spend money on cards and build an actual competitive deck. Again I am not familiar with the Arena meta anymore, but there is a legitimate sacrifice deck in Historic, and in the past, BR sacrifice was also a real thing in Standard (I suspect it fell out of the meta after recent sets however).
Finally, if you want to get an overall view of what's good in the metagame, the default decks are not the place to start. Try instead a website like MTG Top 8 which indexes the winner's metagame.

Warning: there is apparently some wrinkle in MTG Arena's matchmaking algorithm such that &quot;good decks&quot; are queued into other good decks. It is why back when I played, if I queued up with monored, I was odds-on to play against other monored decks. It means that you are in for a shock if you upgrade your deck thinking you will get easy wins against bad decks. I don't know how Wizards define &quot;good deck&quot;, however, and Wizards certainly has good reason not to reveal it or people will game the definition.