They aren't really both correct because it's an historical comparison once the games are complete.
Historically you only need to beat the bottom 3 teams individual totals, not finish in 17th because it's historical data, the event is complete.
It's a super example of interpreting statistics to suite.
Both are factual statements.
In the example we have used above, 2020-2021 season.
If you look top down 33 points would not have been enough to finish above Burnley in 17th who finished on 39 points. Surely you agree with this statement? It is a fact.
If Fulham had gained an extra 4 points and got 33, they would still have finished 18th and been relegated.
If you look bottom up 33 points beats 3 teams so it is also hypothetically correct that 3 teams would be below them. It is also correct that Burnley could have finished on 33 points and survived.
Basically we are adding a hypothetical team into the equation. A 21st team that finishes 18th out of 21 teams. You are saying the bottom 3 are relegated so they would survive. I am saying the top 17 stay up so they would be relegated. Again, both are correct.
In the Championship scenario you are saying the hypothetical team on 71 points beats 18 teams so you are saying they would be in the play-offs. I am saying the hypothetical team on 71 points was beaten by 6 teams so they aren't in the play-offs. Again both are correct.
You are right, this stat can be interpreted either way to suit an argument but they are both correct
Out of curiosity, how many points short of the play-offs would say Boro were this season? 2 or 5? Because I would say 5 as we would have needed to beat Norwich to displace them in 6th. But by using your theory, Boro would have only needed 2 more to finish on 71 and beat 7th place Hull.