Long time watcher of it. Definitely one of the most frustrating shows to watch because it was clear the writers and show-runners had difficulty managing a lot of characters, bound by their own restrictions (No flights, no tights, certain DC characters unable to appear) and not seeing storylines through (The number of plotlines and elements they would just drop or pickup without logic or explanation was maddening). And I didnt quite agree with the fans complaints either when they were picking on certain things like specific characters rather than seeing the larger structural issues of season to season narrative
I see a lot of people give it some nostalgia praise now when comparing to the CW Arrowverse and I think that's romanticizing the past a little. I would say a lot of the current DC shows on TV havent done the major mistakes Smallville did (I feel like they have at least a 5 year plan) but I also think a few of them have fallen into the bad habits of just not knowing what to do and sometimes listening to a fragmented fanbase (Arrow especially)
I dont if it really birthed the current run of shows. In some ways it did, in some ways didnt. Definitely these shows were brought on as a replacement to Smallville and expanded but I dont think they've copied their formula and are better for it (Only Gotham is somewhat similar in terms of having to alter their universe introducing villans early because they were bound by their own rules and didnt have confidence in their own vision of an origin story, which Smallville was guilty)
But I would say Supergirl and Flash are probably better than Smallville ever was and I say that as a serious fan of the show
I don't think people realize that "Arrow" was originally supposed to be a spin-off of "Smallville" starring Justin Hartley.