Ability to merge adjustments + flatten image in LR

"At this point, I feel as if this a cry for help. I know im not the only one who would love to have the option to flatten/merge my adjustments in lightroom; to then be able to apply a preset, grain, crop, whatever else.. its this too much to ask for *cries*. I dont always want to take each photo through PS."

It's not really clear in your post what you are trying to achieve. All of the things you mention, preset, grain, crop, etc can be done directly on the image in Lightroom Classic. And, ALL of those processes can be removed or changed to your heart's content in Lightroom Classic. Even five years from now.

If your goal is to have different versions of your images where those processes are applied separately, GoldingD's suggestion about making "Virtual Copies" is a great idea. You can make as many virtual copies as you want, process any of those copies exactly the way you want and not affect the original edit or any of the other virtual copies. You can find the "make virtual copy" function by right clicking on the image while in the Develop module.

For a Lightroom Classic user, Photoshop is generally only needed when you want to do special things like put text on a photo, move one person's head to another 🙂 or combine multiple images into one.

You can already do that. Export the image as tiff or psd, and check the option to add the exported image to the catalog. Yes, this creates a copy, but that is inevitable. You cannot 'flatten' a raw file to include the edits and still keep it a raw file. For a tiff, psd or jpeg original you could do that technically, but because Lightroom works the same for raw files as for non-raw files, that option is not available just for non-raw files.

Consider using virtual copy's.Accomplish your initial edits, make a virtual copy, the virtual copy will include the previous edits, then edit the virtual copy with your desired changes.

Maybe I do not understand the why in your request.

LrC is a parametric image editing program, edit by edit, instructions are made, and placed in the database record (catalog) for adjustments. 

Photoshop is a raster editing program, each completed edit modifies the appropriate pixels, once saved, the previous pixels are gone. However, you can separate edits into layers. Upon exit or save you can choose to flatten those layers, in effect merging all into one layer, ability to alter those layers is then gone. (not  PS heavy user, others will correct)

For LrC to display your final result, your final edit, it needs to work thru each and every develop module edit, one at a time, from the first, thru to the last. It does this each and every time you add one more edit. Even if you delete the history. Note that some edits, like adjustment brushes are more complex and can slow LrC down, especially if at the end.

So, I do not think so.