Universities admit in batches. Top-tier admits in the first round, second-tier in the second, and vocational colleges later still. Tier determines admission timing more than it determines academic quality.
In practice, the top-ranked national universities all admit in the first tier, and the correlation between tier and reputation is strong at the top. But there are excellent programmes at nominally second-tier schools, particularly in engineering and applied fields.
The elite designation (equivalent of a 'research-intensive university group') is a more current signal of national investment than tier alone.
For most students, the useful shorthand is: which universities have your target course, and where do their historical cutoffs fall? Tier is a starting filter, not the answer.