If Conor Lamb wins it’ll be because of these treee factors ranked in order of importance:
1. Saccone’s incompetence/potential corruption
2. Conor Lamb’s exceptional campaigning ability
3. National environment
Gotta disagree with you there, I think it'll be:
1. National environment (without a historically toxic environment across the board for Republicans, this seat wouldn't even be remotely competitive even with everything else; I'd argue that this is far and away the most important factor. Honestly, Saccone should be winning by like 15% without breaking a sweat even in a Democratic-leaning national environment, IIRC Trump won this decidedly WWC district by about 20 points in 2016)
2. Saccone's general incompetence as a candidate is what may in the context of the national environment may be what pushes Lamb just over the finish line, but the national environment is what made this race close enough that its not inconcievable for that 1-2% Saccone doesn't get due to lazyness/incompetance to be the deciding factor. Anything within single-digits here should worry Republicans and if Saccone wins by 5% or less, then that's still a disaster for the GOP in terms of what it suggests about the midterms. It'd certainly indicate that the "Trump/GOP rebound" narrative is...well...completely baseless. This isn't like the Alabama Senate race where Republicans can just write it off as being about the candidate if they lose. Saccone didn't help, but any Republicans who think this seat is in play primarily b/c of candidate quality are only fooling themselves.
3. Well...actually that's about it. I disagree pretty strongly with you about Lamb being some sort of exceptional candidate. I mean, he's not bad or anything, but he's also nothing to write home about; he's simply an average candidate running a reasonably competent campaign. Honestly, he's not even the strongest Democratic candidate in the district and IIRC was like the 4th or 5th (might've even been 6th) choice to run here. Lamb only became the party's choice after all the top-tier recruits said they weren't interested and there's a reason for that: he's not a top-tier candidate (Lamb is on the weaker end of generic b-list, but Saccone is running such a lazy campaign that he makes Lamb look like a first-rate candidate by comparison). Again, there's nothing wrong with Lamb per-say, but someone like Brandon Neuman or Matt H. Smith would have been a much stronger recruit.