There is a lot to unpack here. Let's begin from the top.
Davey Johnson is brought on to helm a young team and bring them from being regular season losers to being contenders. He is an old guy who was "new school" way back when but largely managed like a manager from the 80s would. He has a two year deal and made it clear that once that deal was up, he wanted to ride off into the sunset of retirement.
Fast forward to the offseason before 2014. The Nats make the playoffs for the first time but miss the mark in 2013 due to injuries mostly. Davey rides off into the sunset and the Nats openly interview managerial candidates who are more "new school" because that is where it looks like successful teams are headed. They seemingly felt that leadership qualities were less important than in game management and let Mike Rizzo hire his buddy Matt Williams. Williams gets a two year deal with two option years after that, reportedly.
Fast forward to the offseason before 2016. Matt Williams, who inherited the majority of the coaching staff of Davey Johnson, is fired because he was awful with managing personalities and was much too cold to his players. Players were more comfortable talking to the old guard and Matt Williams did a great job in dividing himself from his players. His managerial ability was also in question, as he wasn't the SABRmetrician that was originally sold to the team upon his hiring. After a disappointing season where the clubhouse dissolved, he Nats again openly interview managerial candidates but this time put an emphasis on prior success and being a "player's manager". The two finalists are Bud Black and Dusty Baker. Baker has a better track record, but has never been good with X's and O's in decisive games. Bud Black is extended an offer he felt was "low ball" and does not take the job. The offer goes to Baker, who takes a 2 year, 4 Million contract with no option years.
Fast Forward again to the offseason before 2018. Dusty Baker is NOT EXTENDED. He brought back to back division victories and back to back first round exits. He was well liked by the players, but those same questions about his managerial ability ultimately caused him to not be retained beyond the initial contract. There was always this possiblity and although the ownership handled his dismissal very poorly with timing, Dusty Baker not being retained should not have come as much of a shock as it did. The Nats, again, openly interview managerial candidates and hire Dave Martinez, the right hand man of Joe Maddon for years who has been the defensive positioning coach and lineup creator. He is well respected by players and other coaches alike.
These are the facts as we see them. Unless I forgot something, please correct me.
The major gripes seem to be that people think Dusty is less of a gamble than anyone else but fail to see that Dusty is such a known commodity now that you can almost pinpoint when he will "outmanage himself" in a big game. It's more of a gamble to HOPE that Dusty figures out how to get over that hump than it is to throw in the chips on a less known manager. Sure, things can go pretty wrong, but this hire is more unanimously liked than Williams was, and there is a track record of young managers with little experience doing well.
Let's not say the sky is falling until it is.