Concept Bikes & Bike Innovation - for better or worse

As for 3D printing, I am wondering... Does it produce structurally strong pieces (compared to forged metal, for example) ?

Not as materially strong as some traditional metalworking processes, although the best additive manufacturing processes can get pretty close, and make up the deficit by more precisely putting the material where, and only where, it is needed, so for a given mass, the structural strength can exceed legacy methods, since some complex forms simply can't be made by traditional processes so the final component retains some essentially redundant material which traditional tooling couldn't remove.

If your legacy process was casting (as it was for high end frame lugs), I think Selective Laser Melting might actually be able to produce better results, as there is potentially tighter control on the cooling rate.

As for 3D printing, I am wondering... Does it produce structurally strong pieces (compared to forged metal, for example) ?

It does but with some significant drawbacks. While the grain size and structure can be well controlled. With titanium for example, some electron beam melting methods, such as Arcam, can produce a bulk material with better properties than the wrought equivalent. Assuming you get consistent melting through the layer. However, the major drawback is surface finish, which is generally terrible and a function of the thermal conductivity of the metal. Macro and microscopically extremely rough. While for the most part these rough surfaces can be machined or precision linnished off this can only be performed (at significant cost in both time and money, which can defeat the obtect of rapid prototype manufacturing methods) on external surfaces. So when you have a nice complex structure where material is only placed where it needs to be, if there are surfaces that are internal, enclosed or unreachable it leaves a really poor surface riddled with pits and holes that are excellent crack initiation points. This hugely limits the fatigue life of such a part. This is something most people don't realise or even address but is the reason such parts are not used, in F1 for example, for fatigue critical parts but may be used for components such as the roll hoop, which is highly structural (in the event of a roll-over crash) but not subjected to any fatigue loading during its life.
This surface roughness factor, which can go as deep as 0.5mm or more, can have major implications on achievable component wall thicknesses.

tldr: yes and no.