The mechanical effect of importation is it lowers the potential results of two rolls: having any of it being made and total quantity available. Theres not going to be a real expense level as you might be used to from most arms race games, and difficulty of production is unaffected by it, except potentially at first(depending on how you go about getting plans for them, i.e., reverse engineering in a factory or buying plans/reverse engineering on your own).
Why you might not just spend the extra effort to create new equipment, that is indeed an option. As for why, well, you can use slightly different resources for it and it will be faster.
As for why I am using a system so old for the starting setup, because it gives you lot the opportunity to shape initial equipment instead of, for example, my going "yall be french now" and dumping a load of obsolete french crap on you. As you have looked at the other games using the same setup, you can see that it is only used for initial equipment, as is being done here. Yes, the spread is greater, but then there are nations still using pre 1900s equipment for their armed forces, and I wished to give that opportunity to you lot, considering this isint just you equipping the front line troops, but the entirety of the nations security apparatus. The increased prices due to greater timespans are an unhappy side effect of that, but also accounts for the nation being a comparably backwater area for most of its history until you lot, each with your own companies and negating the sometimes decades long development process of equipment, came along. So, yes, you are being encouraged to buy old outdated shit, because five turns after combat starts Im probably going to see you shoving people in autocannon equipped power armor even with this.