Is it just me or is the LRc HDR functionality useless?

I would agree, when I join my photos together it is EXACTLY the middle photo. Super frustrating when I am trying to do real estate on a sunny snowy day, all windows are now overblown because it will not work.

when I HDR merge the dng file generated doesnt have the dynamic range that the original file has, for example the overexposed area cannot be recovered while the original underexposed file(bracket) can, i shot 3 photos of 1ev，it used to be working.

Have been following this thread, and just had to have a go at your images!

My quick result using only two of your frames.

A linear gradient from the left pulls up the left of frame.  A circular gradient brightens up the area of the door. Highlights & Shadows adjusted as suggested by @Bob Somrak  Adobe Color profile.

"The biggest time sink for me with the LR version was having to apply some exposure brush strokes to adjust parts of the image that still needed some exposure comp."

This shouldn't be necessary for the majority of LrC generated HDR files. In my example with five 2EV bracket image files no local brushing was applied, just the global Tone controls in the Basic panel. Try using -100 Highlights & +100 Shadows and then adjust the other controls as needed. If the HDR file still needs brushing I suggest uploading the bracket set to a file sharing site and we can take a look. Concerning disk space once you're happy with the adjusted HDR DNG file you can delete the bracketed image files.

Ok, so I guess I owe LRc HDR function an apology 😉 It does work, I just need to adjust the image as others have pointed out here. For now I'll probably stick with the software i currently use to generate HDR images. It's just easier to work with batch files in that program. And I already know how to get the look I want using that system. I would say it's also quicker for me to edit the generated HDR images in the other program, but I know if i used LR for an extended period to create my HDR images I'd cut down on the editing time there as well. The biggest time sink for me with the LR version was having to apply some exposure brush strokes to adjust parts of the image that still needed some exposure comp. With the other program I use I pretty much never have to do that. And there's also disk space savings since with LR it's basically going to double the amount of disk space required if i want to keep the original bracketed shots alongside the HDR merged image.

Thanks to everyone who posted some helpful information here. If nothing else it forced me to reexamine how I process photos in LR. It's always good to get out of a rut and try things from a new persepective. 

"It is truly a high dynamic range I'm working with. Usually with a dimly lit interior and a bright exterior outside a window. Or occasionally an exterior scene with bright sunlight and hard shadows. In most cases I usually do 2stops of exposure with 3 images, sometimes 5."

A wider dynamic range image is going to require more bracketed files. Using more backeted image files is going to require more extreme Basic panel Tone control adjustment to get a good looking image. Below is an example using five 2EV bracketed image files. On the left is the HDR DNG file with no adjustments applied, which looks pretty crappy! The image on the right is with the adjustments showing in the Basic Tone control panel and no other settings applied. I created an article with suggestions and tips on using the Tone control adjustments, which may be helpful.

https://helpx.adobe.com/lightroom-classic/help/tone-control-adjustment.html

Thanks for the replies from everyone. Sorry I did not respond sooner, I didn't get any notifications that there were any replies. 

Just to clarify - i'm not trying to get a 'grunge' look or anything. It is truly a high dynamic range I'm working with. Usually with a dimly lit interior and a bright exterior outside a window. Or occasionally an exterior scene with bright sunlight and hard shadows. In most cases I usually do 2stops of exposure with 3 images, sometimes 5.

I'll post some example images tomorrow to show you what LRc is generating when let it do an HDR merge.

Yes, I think that must be emphasized. HDR is not a gimmick to get grungy pictures. That has nothing to do with HDR, but with (bad) tone mapping. Tone mapping is also used in HDR after images are merged, to get back to a normal dynamic range, but they are not the same. You can tone map a single image too, and make it just as grungy. These images are often called "HDR", but they have nothing to do with real HDR.

Real HDR effectively extends the dynamic range of the sensor. There is little or no reason to use it if the scene your are shooting does not exceed the dynamic range of the sensor in the first place.

There has to be a substantial difference in exposure between the shots, see post by @JohanElzenga .

I find LR's HDR function excellent, here's a typical example of an interior with a window.

I use it a lot, and find it generally does a good job; however I usually tweak the sliders a bit after the HDR is generated to reduce the highlights and lighten the shadows. It does NOT provide that over-processed grungy effect that was so popular a few years ago. In fact, I've re-edited many of the HDR's that I previously processed using Photomatix and have deleted the Photomatix version.