I guess it depends on how you quantify success, it seems to me most owners/fans would quantify success as winning Super Bowls or at least getting to one or at least getting to Championship games or at very least wining playoff games.
Cowboys report card for the last 20 years on those measures of success:
Winning Super Bowl = 0 last on 1996
Getting to Super Bowl = 0 last one 1996
Championship Games = 0 last one 1996
Playoff Game Wins = 4 have a losing record 4 and 9.
So if winning regular season games is your measure of success (I think it is Jerry's) have at it you have a right to that opinion.
But for me it is getting too and having success in the playoffs.
Any GM in the league would have been fired a long time ago for lack of playoff success and the roster construction that caused the lack of success in the playoffs.
So yes I would say the Jones have not been very good at roster construction to achieve playoff success..