Neither of those two things are quite relevant. Senators don't have "seats" to speak of (i.e. the distinction of which class a senator is in is not relevant) and MA had a Republican Senator consistently until whenever Paul Tsongas beat Edward Brooke, and the existence of the Solidly Democratic South has little bearing on the plausibility of electing Democrats today. At the time where Democrats won the South they had total capture of machine politics, conservatives routinely ran as Democrats to get access to the party machinery, in many cases there weren't even Republican candidates for house seats and in some cases not Senate seats. But voter self-sorting, the nationalizing of politics, inter-party polarization, etc. have all contributed to a very different structural reality today. The Democratic Party of Alabama has essentially no resources, whether economic or human. Even popular Democratic incumbents are losing their grip on power in the Southern and Appalachian states and it's unlikely the party will be able to do the investment required to rebuild. They also have no talent bench because of the extremely rapid Republican takeover of state houses and senates over the last 20 years. And the Demographic trend in Alabama is not favourable like it is in, say, Arizona, Florida, Georgia, or Texas.
The good news is that Democrats can easily have 60+ Senate seats without winning Alabama.
In a vacuum, we'd imagine that Colorado, Maine, Nevada, Ohio, and Wisconsin would be fairly easy for Democrats to win with decent candidates and national tailwinds, and after that Florida and maybe Pennsylvania if the entire state doesn't die of heroin overdoses. Pickens get pretty slim after that, even with increased investment in long-shot seats. And long-term the Democrats will lose West Virginia, it's just a matter of time.
