Doh, I should have spotted this right away. You tell PM to have the DNG converter produce Linear DNG files. That is causing the huge increase. Turn that option off and you should see much smaller files.
Note: unless you have a specific need for this, you should never convert to Linear DNG! Linear DNGs aren't really raw files, but contain
already demosaiced image data, thereby losing the ability to benefit from any future improvements in the demosaicing algorithms.
Regarding the resolution, I did a little digging and from what I found, the DNG converter does not set this at all. It simply leaves the resolution at what's already in the file (which is good as you are just converting the data to another format, not change the metadata).
What baffled me though was that in the file, the resolution seemed to be set at 300, but PM showed it as 72. Weirder still when I then instructed PM to set the resolution to 300, it showed it as 300, but the underlying metadata (as inspected with exiftool) hadn't changed at all…
But it gets more funny: I then quit and reopened PM, et voila: the resolution once again back at 72ppi
(at least this does explain why exiftool didn't find any differences
)
@Kirk, this seems like a bug to me. My guess is that PM does not correctly interpret the DNG resolution data (which is in the makernotes).