It’s true, but only to some degree. You get these unwanted items, but you can craft them, even so rarely.
Furthermore sometimes you end wipe without researching full tree, so the next wipe you might decide you tech tree the item instead of opting for roaming to get it. Don’t get me wrong, such mechanic can be fun part of the game, knowing your effort from the last wipe payed off in some way; on the other hand making tech tree more expensive per item won’t deny you that, just make it a bit less useful at the start of a map wipe, but might create mindset “it’s pretty much always worth roaming”, thus making entire wipe more eventfull.
And additional benefit would be community servers that have some extra default BPs unlocked would still have roaming as a better way to get BPs than using the tech tree.