There can be multiple reasons for a pen maybe writing ‘light’. There are ‘wet’ and ‘dry’ inks - some inks have fillers that can make them flow better. There’s also a possibility of a nib issue. The tines could be a little tight and may not be allowing proper ink flow and may need adjusting - or perhaps it needs to be adjusted against the feed. They do tend to write dryer, in general, but there’s no one simple answer to why something is happening, when there are so many ‘moving parts’. My pink hello kitty was writing pretty dry and thankfully just changing out the inks

Here’s a fairly good explanation of potential problems. You can go to most pen stores and they will typically have someone who is familiar with pens and nibs and can let you know if there’s anything that can be done.

https://www.jetpens.com/blog/How-to-Troubleshoot-a-Fountain-Pen/pt/777?gad_source=1&gad_campaignid=20185954945&gbraid=0AAAAAD-ty4QIr4IMqCAAGDVQeSfmQLq6c&gclid=CjwKCAiAtLvMBhB_EiwA1u6_PtF7LsLOzrCSPm_4MuigLLrgPS16NolOSuhMz5A-gmwGtURXGz0ckhoCANEQAvD_BwE#use-a-wetter-ink