Can't miss what you haven't had. I'm not sure what mfrs other than Samsung use the separate lock screen ... I know I had one on one of my older phones but haven't had one for several years and haven't really missed it. IIRC, when I had it, notifications weren't as readily accessed and the lock screen I used pretty much served that purpose.
On a scale of 1-10 for things I'd like, the lock screen might be a 2.
I moved from a Motorola Droid Turbo. I somewhat miss Motorola's feature set but suspect it's more reverberations of change than a gaping hole of "really miss". I'm willing to suffer that loss for gaining immediate access to Marshmallow and future updates.