Hi. I do a hit of cycling and use and Edge 530. I also have an Instinct watch. I know I can link the HR off the watch to the Edge, however, rather than doing this why don’t you upload the data when the watch syncs.

There s a reason for that. Garmin uses such system, where the device is the central "brain", and the majority of data is being generated and processed directly on it. It is not done on the server (or by the GC app), it is done directly on the device. It includes Calories burned, Intensity Minutes, diverse personal records, VO₂Max and Training Effect (not in case of Instinct alone, though, which does not support VO₂Max), and a lot of other data. Even the acquiring of GPS keypoints depends on the changes of the HR (in the Smart Recording mode).

Hence, when the device does not have the necessary data (the HR, and the HR Variability data, in this case), it cannot properly generate the data. Merging them later, in Garmin Connect, would not make the same effect, and it would be also complicated if any of the separate devices was not perfectly time-synced. For all those reasons, linking the watch (or a HRM belt) with Edge is highly recommended.

I too have an Instinct & 530.  For a large percentage of my rides I broadcast the Instinct HR to the 530 instead of wearing a HR strap.  Very simple and as trux explained pulls the HR data seamlessly into the activity data stream.  I'm always wearing my Instinct anyway which makes this setup very convenient.  I typically use the Broadcast Heart Rate control.