P: Equalise photos in a panorama tool to match all to the chosen reference shot.

​@Merlin3, like ​@drtonyb and ​@JohanElzenga, my experience with LR’s Photo Merge > Panorama is generally very good at blending significant differences in exposure. 

If you’re observing something different, it would be good if you could share here an example set of original files to be merged, so we could see exactly what you’re seeing and experiment with alternatives. It they are too large to attach here, then upload them to Wetransfer, Dropbox, Google Drive or similar free service and post the sharing link here. 

I have to agree with ​@drtonyb that Lightroom Classic panorama merge is actually very good. The only problem I have found is that you should not apply the Adaptive profile to the brackets before merging them. That can cause severe unevenness in the merged panorama. Apply a standard profile like Adobe Color, merge the panorama and then -if you do want to use the Adaptive profile- apply it to the merged panorama.

​@Merlin3 

There is even more to this; LrC has a bug with Auto Importing the DNG from Pano Merge (and from HDR Merge, and files returned to LrC from Edit In...).

This bug has been around for years and despite reporting it numerous times, absolutely nothing has been done to fix it. Records for the returned files are not being updated correctly in the catalog.

​@Merlin3

There is more to the LrC’s Pano Merge. I shot three photos as a pano sequence with the first shot underexposed 2 stops in the camera, the second exposed normally and the third overexposed 2 stops.

With no LrC Develop adjustments, I pano merged the three photos:

Despite the overexposed shot being the target photo, the merge in LrC has equalised the exposures so the result looks normally exposed. If I try pano merging these three shots in Photoshop, the result is a ghastly mess.

My conclusion is that LrC’s pano merge is doing a very good job, even when faced with varying in-camera exposures.

​@Merlin3 

LrC matches the Develop settings of the target photo to a selection when doing a Panorama Merge; it does not match changes due to in-camera changes to exposure.

For example, the screen shot below shows the LrC Pano Merge of a selection of photos, and as seen in the Filmstrip, some I have set Exposure to +2.00, others have -2.00 Exposure, while the target photo is adjusted to look normal. In the Merge Preview, all the photos in the selection have been matched to the target photo’s settings. 

Without seeing what you are using as the panorama series, it’s difficult to give any more advice.