Linseed oil and various commercially available spoke preparations are not required to build a good wheel, it is the tension that is important.
This tension needs to be achieved without creating spoke wind-up, where the spoke is twisted in the process of tightening it, wound up spokes will unwind in use and become loose. Using a lubricant like gear oil on the spokes and spoke holes will help reduce wind up as will linseed oil but linseed oil also acts like a thread locker which reduces the opportunity for the nipples to back off when the spoke becomes loose. If the wheel is well built in the first place you do not need this thread locking quality as the spokes will not come loose. Having a nipple that does not unwind on a loose spoke is not a sign of a well built wheel.
I have built wheels with and without a lubricant and the only difference I have found is that the nipples are less likely to become siezed later on the lubricated ones so truing the wheel after it has been in use a long time is easier. It has made no difference to their longevity.