I'm not sure I agree. Building a championship decimates a farmsystem in two ways -- by promotion, and by providing fodder for trades. There is a goal of GMs to maintain a 5-7 year window of sustained success by a combination of smart free agent signings and limited poaching of talent from the minors, but indefinite success, or trying to have your farm system cake and eat it too, is not something that any GM, no matter how competent, can sustsain indefinitely.
Time and time again history has proven that while you can build to win at a high level for a few years at a time, ultimately your alternatives are to invest your resources in building a winner, or not having a winner.
If you're good you can put it off for awhile, but eventually you have that choice -- Go For It, or Don't. And each choice has significant long term consequences, as we saw in 04 when we went in with both feet and struggled for a few years afterward, and as we saw in 14-15 when the emphasis was on rebuilding the pipeline and the results at the big league level were extremely unsatisfying for fans and ownership.
Ultimately it's a herculean effort to maintain either a top farm or a championship roster. Trying to do both at the same time is either an act of genius, or an act of lunacy, generally tending toward the latter.
That said, I'd love you to produce historic examples of teams that prove me wrong by having nearly indefinite success without ever disrupting the pipeline.