What were Jaylen Brown's WS/48 the first 46 games into his career? I bet pretty unimpressive, and I have no idea what WS/48 means, although it probably is a sophisticated measure of value relative to minutes played.
Jaylen's per-36 for his rookie season (total 1341 minutes played averaging 17.2 mpg) --- 13.8 pts 5.9 reb 1.7 ast 0.9 stl 0.5 blk on 53.9% TS.
Slicing it thinner, Jaylen averaged 8 points per game the first month of his rookie season on 62.5% TS. He fell off a bit the next few months, then jumped up to 10.4 pts per game on 60.6% TS in February. He closed out the season with two more months around 8 points per game.
In short, Jaylen really just is not a good comparison here. He came into the league as a fairly productive, if limited player, and has simply added more to his game and to his capacity (more minutes, more shots, more ballhandling, etc), with each passing season.
WS/48 refers to "Win Shares per 48 minutes." It's a way of measuring overall impact on the box score + wins/losses on a per minute basis.
Hyperproductive players end up around .200 or better. That's Rob Williams.
.100 means a player is pretty good.
Below 0.050 means a player is either a defensive specialist or just not really doing much out there.
You're right that it can be problematic to pass judgment on a player too soon. However, Nesmith is still in his rookie season, and even before his more productive outings recently, he at least made sure you noticed him out there with his hustle and energy. Nesmith is also a guy who has really good shot mechanics, which offered reason to trust that his jumpshot would come along even when he has struggled at times. That logic doesn't always work out (see Ben McLemore), but it's different from a guy like Langford who fell in the draft in part because of questions about the basic mechanics of his jumpshot.
So far Langford is more comparable to someone like James Young, who came in young and raw and struggled to stay on the floor or produce from day one. Now, I think the reasons for that are different in those cases. But in terms of on the court impact, they're not far apart. Langford at least has shown flashes of on-ball defensive ability, but it's hard to roster a guy based solely on his potential as a wing defender. There are undrafted players available every year who can offer that package. Javonte Green is an example. Javonte is a much more polished offensive player than Romeo at this point, honestly.