Nope, equally weighted doesn't mean that one UMAT point is equal to one ATAR point. It means that your UMAT ranking and ATAR ranking are given equal merit.

For example, if I were to oversimplify the system, then, if you have a 99.80, you might be ranked 200th in terms of ATAR (say), and with your UMAT of 172 you might be ranked 400th, for an average ranking of 300.

The system is a bit more complicated than that, and uses z-scores and calculations of standard deviations etc. to actually qualify this, but an ATAR of 97.30 is way, way, way down the ranking list compared to a 99.80 rather than just a couple of points - there are at least several hundred people ranked between the 97.30 and 99.80. Consequently, you'd need a UMAT ranking which was much, much higher (several hundred ranks higher!) to get an interview with that.

As a rough estimate, a 97.30 ATAR has generally required a UMAT around the 205-210 mark for an interview at UNSW, and this would be scraping into interview (and consequently also having a very low chance at getting a place due to competitive combined scores being much higher than that.)

If your above system were the case, then given that a 99.95 with a score of 152 gets an interview ( - total 252 by your system) then a 50 ATAR with a 202 UMAT should also get an interview (same total 252 score) - this makes zero sense.