Compared to a couple of the other trades that Lombardi made (a 1st+McKeown for Sekera, Cernak for Ben Bishop), this trade was a good one. I contend that it was the right deal for the Kings to make at the time.
Everyone mis-remembers what was going on with Martin Jones at the time of this trade, and just say "oh they gave up a starting goaltender for no reason."
Back in 2013, Martin Jones held out into the start of rookie camp in September because he wanted better terms on his 2nd contract after his ELC. Lombardi didn't back down and Jones finally signed on September 11th. Here's the roster for the first game of rookie camp, which should have featured Jones as the starting goaltender for the Kings:
2013 Kings Rookie Camp Roster
We all know how Lombardi felt about contract holdouts after seeing his reaction to Cammalleri and O'Sullivan. He wanted players to go about negotiations "the right way," and was very irked by a goaltender who had yet to play an NHL game missing camp over contract negotiations, even if he had put up stellar numbers in the AHL.
Fast-forward two years, and Jones was ready to do it again. He now had 34 games of NHL backup experience, including a stint where he split time with Ben Scrivens as the starter while Quick was down with an injury, putting up insanely good numbers. He also got his name on the Stanley Cup in 2014. With the Kings already having cap issues and having to let Justin Williams walk, the Kings weren't prepared to give a multi-million dollar contract to a backup goaltender. He had to go.
On the flip side, Milan Lucic was exactly the Darryl Sutter-type player that the Kings had been looking for. Factor that in with the team missing a bonafide 1LW for 5+ years since Frolov departed, and the Kings wanted to fill that gap. After winning 2 Cups with Brown filling in on his off-wing, they felt that this was a chance to acquire that #1 guy, especially with Brown playing poorly for two straight seasons (only 27 points in 2013-14 and 2014-15).
To Lucic's credit, he came in and scored more points as a LW than anyone had since Frolov departed, putting up 20g and 55p. He was a wrecking ball on the ice and often came to the defense of his teammates. He was exactly what the Kings had been missing. He wasn't great in the playoffs, but was 3rd on the team in scoring behind only Kopitar and Muzzin, with 3 points in 5 games (0+3=3). Contract negotiations came up in the summer and the Kings tried to re-sign him, with the Kings offering him an 8 year, $32 million contract, the max they felt they could afford at the time. He turned it down for more money and a chance to play with Connor McDavid in Edmonton. We all know how that went.
However, in hindsight, I would say the Kings made the right deal at the time. It's anyone's guess if Lucic would have declined so quickly had he stayed in LA. Lucic demonstrated chemistry with Kopitar and was playing well before he left for Edmonton. Edmonton seems to have the capability of destroying players' careers.
So to recap, the Kings shipped out a disgruntled backup goaltender that was going to hold out, a defensive prospect picked in the 5th round that looked promising, but had yet to play in an NHL game, at a time when the Kings had an embarrassment of riches at defense (both Forbort and Gravel were ahead of him on the depth chart), a mid-round 1st during what they thought was the height of their dynasty. In exchange, they got a player that came in and played exceptionally well, but couldn't eventually work out an extension for (thank god).
Eventually, the trade wouldn't really work out for either team. Miller left Boston a couple seasons later in the expansion draft, the 1st turned into a bust (yes Zboril is a bust), and Jones was flipped immediately and signed a $3M extension a few days later. Jones returned a nice haul to Boston (Sean Kuraly and Trent Frederic), but there's no way that the Kings and Sharks, two teams with recent bad blood from the playoffs, were making a trade with each other for a starting goaltender.
So if you want to say who won or lost, it's really hard to say. The Kings got a quality season of Milan Lucic that met (if not exceeded) expectations. Boston got two okay seasons out of Miller, a quality role player in Kuraly, and a prospect that could turn into a quality player for them (Frederic). The arguments that the Kings could have gotten more for Jones are disingenuous.