player ID and skin error from new launcher

Since the new launcher (2.0.729) downloaded itself recently I could enter one of my old 1.7.10 worlds but all my achievements and stats were reset. I looked in the playerdata files and apparently whenever I start the game using the new launcher it gives me a different player ID rather than the one I have used for the past 5 months. (29e111cc-db36-4ca3-b103-1d81fe68caa7 is the 5-month old one, the new one from the launcher is 413af1b3-26d8-3d1b-96d6-652a6996c3f8) When I rename the player files and the stat files all my stats returned but my skin still cannot be changed even though I change it on the Minecraft website. Strangely enough, I tested my profile from the MultiMC launcher just to see what happened, and it used my old player ID and old uploaded skin even for a new map. Somehow, the new launcher forces me to use a new ID which doesn't accept uploaded skins while the third party one has accurate data from the online servers.
I have problems with MultiMC and thus would rather use the officially endorsed launcher, but the new one doesn't work and I can't seem to restore the old launcher using a restore point.

P.S. I saw in another recent (somewhat angry) post that the new launcher is on "6% rollout" and the new launcher isn't forced upon anyone, but my searching skills are apparently lacking and I cannot find the old 1.6.76 java launcher version for download. Could you tell me where to find it? I would rather use the stable, older, simpler, less-windows-10-style version.