1 and 2 gears are exactly that. Your car won't shift out of that gear until you manually shift it. If you go down to 1, you will literally go 10 at 6000 rpms. Don't pull down into these gears at high speeds or car go boom lol.
A harder shift is actually better for a auto trans because automatics, when the shift, are technically in 2 gears at once so to speak which is why shifts are usually smooth with an auto.
That said, with a factory shift tune, and components, some things will take more of a beating shifting manually. Plus shifting manually with a stock auto is pretty useless, multiple second delay between shifting the lever and actual shift.
Look into an older hydraulic AOD with a forward manual valve body and a ratchet shifter.. hell of a lot of fun and the shifts are hardd lol only downside is with a manual valve body vs a shift kit is you have to manually select gears, no put it in D and go.. lol