Imo Teheran & Wood are legit, even though I stated my opinion several times in spring training that it will be interesting to see how Wood will do late this season: He only pitched around 140IP last year between AAA and the majors and before he was put into the bullpen, had two bad starts in early September. So he might hit a wall, once his IP total gets to 150+ in August/September.
Otherwise I can see Teheran putting up an ERA around 2.75 and a 1.15 WHIP, Wood somewhere around 3.25/low 1.2X. So if Minor can stay healthy (imo a big "IF") that + Santana (who should at least give them a bunch of quality outings and put up a low 3.XX ERA) would give them a very good rotation from 1-4, maybe without a true ace (imo Teheran is close to that), but four quality arms that can keep you in pretty much any game.
Harang's numbers though will plummet, also not sold on Floyd.
Overall I think I overrated the loss of Medlen a bit because I didn't think they would really go after Santana to replace him. Beachy isn't that big of a loss if you compare them to last years team simply because he already missed almost all of last season, just making 5 starts. I also didn't put that much value into Hudson's loss because he only gave them 130IP with an ERA of 3.97, numbers that full season of Wood in the rotation + maybe David Hale or Floyd should be able to reproduce. So after all is said and done, I think right now with Minor back in the rotation, their starting rotation is not worse than it was a year ago.
BUT: In contrast to last season they lack depth, so if Wood hits a wall later this season or Minor gets injured again, they will feel that loss. They also lost a couple of very good bullpen arms and their pen doesn't seem as unhittable as last year. And imo their pitching also suffers a bit due to the loss of McCann because Gattis isn't as good defensively as McCann was (esp. when it comes to pitch selection/calling a game), but that's just my opinion.
Major problem imo is their offense, they started the season winning lots of games thanks to insane ERAs by their top4 pitchers (Teheran, Santana, Wood, Harang) and a couple of HRs. But if your lineup is so insanely undisciplined at the plate and getting on base at such a low rate, you will go on several prolonged losing streaks because your pitching just won't keep your opponents at 2 or less runs every night. That's even more true if your only really good hitter so far (Freeman) goes into a slump.
And don't forget the division, they're playing in: Every single team in that division can pretty much send out quality pitchers every single night (Strasburg, Fister, Gio, Zimmermann, Fernandez, Eovaldi, Hamels, Lee ...plus you get more than decent guys like Burnett, Wheeler, Mejia, Colon, Alvarez, Koehler), so even with a (still) well-rounded starting rotation the Braves don't really have an advantage in that department.
So what's happened to them? In my opinion: They lost some depth, their bullpen lost quality arms and the major differences are that the Nationals after a down year should rebound (esp. once they get Fister back, even without Harper) and the rest of the division also is improved if you compare them to last season (not saying that the NYM offense is great or PHI is a very good team, just that they look way better than their 2013 counterparts. And maybe I'm overrating their April, but I think MIA seriously might have a shot at getting to 80wins thanks to their rotation + Cishek and the addition of Salty & especially McGehee and some other young guys taking a step forward).
So after winning lots of close games last year thanks to their bullpen & the division being very weak offensively, this year more of those close games might go against the Braves.
Having said that: Let's not forget that they currently have the 4th best record in the NL and the 6th best record overall despite losing 6th in a row. It's a long season and streaks like that happen, but if they want to get close to 90 wins this season, imo they have to figure out a way to increase their OBP. Currently they are 27th in AVG & OBP and a sub .300 OBP just won't cut it, even less when you rank 4th in Ks which means fewer balls put in play (still rank in the middle of the pack in GIDP though) and less runners being advanced on groundballs.
One more thing about the Braves: The order of the lineup. I just don't understand why f.e. BJ Upton is still hitting in the #2 spot. Yes he has speed and yes, he even owns the 3rd highest OBP (a measly .303 OBP though) of the teams regular position players, but he just hits .213 and strikes out at an insane rate which means, that pretty much any other guy should be able to advance your baserunners at a higher rate in front of Freeman than BJ does (fwiw, I'd like someone like Simmons or maybe Chris Johnson more in that spot).
But that's not really worth getting into because if you put up AVG/OBP & K numbers like the Braves so far, you will struggle and it doesn't matter much who is hitting in which spot.
If you want to know what's wrong with them, just watch today's game vs Bumgarner. Guy comes in with a high WHIP, struggling with his control and missing his spots today, too. It just doesn't show up in the boxscore tonight because several Braves (Heyward, BJ, Gattis to name just a few) once again chased bad pitches way out of the zone and thereby transformed would-be walks into strikeouts, helping Bumgarner out of possible jams and killing any possibly promising rallies.