Mechanically, I think you're pretty much spot-on there, Razaketh would probably be a better match thematically and for the Baron's power level than the version we got.
And again, I do want to reiterate, this version of Sengir was very strong in Commander Legends limited. He was great for that context. Unfortunately, he doesn't really fare as well in constructed commander, where there are any number of other options that offer more flexibility or are more cost-effective. He's not unplayable, but he's going to be niche more often than not. For the same cost, I am much more likely to want to slot Massacre Wurm into most decks before I would the Baron (both are actually in my Szat/Kodama deck, but if I had to choose just one, I think I would go with the Wurm).