Dr. Smith, in the old show, started out as a serious spy and saboteur before he became a silly, camp villain. Parker Posey's Smith has different motivations but otherwise could be seen as a direct continuation of the sinister original version that only existed for a few episodes. In many ways, they are *remarkably* similar even though the character has been sex swapped.
Personally, I love that direct connection, but I can understand why some newcomers to the show find the new Smith lacking in motivation. These days, you don't get many villains who are so, well, straight-up villainous. I do wonder how they will sustain the character going forward, but I have faith the showrunners will find a way, and that they will tell us more about her as we go along. (It's the sort of trust I lost for Discovery, and it's nice to have it back.)
I like this show enough that I'm going to stick with spoiler text for your other question.