yeah that could work, would probably still be a bit hard to do. I dont think a PRV can fail in a way that makes output from the geyser poor, it would just either not release pressure or it would leak constantly
If it were me I would honestly start by the tap with the biggest problem. Does it have flex lines or is it hard plumbed? If it has a flex line, remove the flex line at the small shut off valve and attach a new one and test its flow/pressure into a bucket. If it is good or better than the tap, then you know its in the tap or the flex line (It is possible all taps got something in them, I know you its probably best to look for a single point of failure but this is an easy test)
Try blow through the flex line still attached to the tap (with the tap open on the hot all the way, is it easy or hard?
close to the tap it could be:
the shutoff valve
the flex line
the tap
lastly, the pipe that burst, what pipe was it? galvanised? a hot water pipe after the geyser? what did they replace the affected section with, copper? how did they connect the copper to the galvanised?
Sorry for the wall of text