In that aspect you're wrong. If not all the materialized objects and materialization users wouldn't be able to achieve their techniques. How you train then to make an armor that can resist the heat? It's years of technology. Or how can you make a weapon that HAS A PERSONALITY. Or how can you make a black hole. Or a whole building in the case of Novu.
I'm not saying you do that instantly, but the same training that Kurapika did for the chains can be achieved for ANY object because the size is not a variable in imagination.
Huh?
http://www.tenmanga.com/chapter/HunterXHunter106/153245-13.html
http://www.tenmanga.com/chapter/HunterXHunter123/153273-7.html\
In both links it's blatantly said that it's the actual visualization process that takes too long, not the process where you install restrictions and pledges on the Materialized items. Once a thing is successfully materialized with ease you can put whatever restrictions you want, which shouldn't take long (explained later). Just watch the old anime for reference.
You don't train things to make them heat resistant, you put some restrictions on them. I thought that was painfully obvious. Putting restrictions on materialized items has no relevance on the level of technology you have. What takes so long is the time to materialize an object because of obvious reasons.
We can also say those "Memory Points" Hisoka once mentioned when you try to create a Hatsu can directly affect which items you can Materialize in the normal way. If you Materialize an extremely complicated object, you could go insane before you complete it. Subs are complicated, not to mention huge, so why bother Materializing the damn thing when you can buy one?
It's wrong to assume that putting personality on objects goes through the same process as putting restrictions on objects. Personality has a direct relationship to the proximity of the user to the Manipulation Hatsu. That's why it's said that it's so complex to put personality on Materialized livings things like Kastro's double, especially for a Reinforcement user like himself.
http://www.tenmanga.com/chapter/HunterXHunter108/153248-3.html
This is where Kurapika explains which restrictions he puts on some of his chains, like Judgment Chain. It's just a basic reasoning process for someone to put restrictions on Materialized items, depending on their determination.
Size is a determinant for Materialized things because anyone could've just Materialized the whole planet they live on if they wanted to. Only Kurotopi's ability has blatantly said that there's no size limit for his copies. If you're taking the same path as Kurapika did for materializing a submarine you have to know the ins and outs of the submarine enough so that it works like a normal sub.
@Phantron
It doesn't matter if copying a Rose is broken or not, the fact remains that Kurotopi can copy it with no problem and once he gets his hands on one he can nuke the crap out of the planet. It's even said that Kurotopi's copies has no size limit so he could copy the friggin' planet if he wants to. In short, Gallery Fake is damn broken.