I'm starting to think that it doesn't replace the Steam launcher as much as I thought at first.
When I launch SSE for the first time after booting up the PC, I still get the contact to Steam. But for all subsequent launches, it's much faster, and there doesn't seem to be any Steam linkage. Before, Steam client would nag me to go online each time, and now it's straight to the Play/Settings/Quit menu without that.
Whether the Bethesda launcher is keeping an online connection alive, I haven't investigated, but I doubt it. It would need to connect to look or mods, but you can't tell if it does so when you select that option, or at start-up. I haven't pulled the plug to find out, mainly because it's out of reach.
However, I need the Bethesda connection for converting and upload mods for Xbox, so the Launcher is more relevant there.
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I'm now trying to decide which mod comes next. I may just repeat the order I built them. I won't bother with the outfits, as they'd really need higher-res textures for SE. That consideration may lead me to holding back on Khajiit HF until I can do a better canopy texture.