Hoskins and Altherr are good evidence we can grow hitters.
Crawford and Rudolph that we don't have a clue.
Though Williams and Alfaro should drive home that plate discipline/batting eye is as important as raw skills (bat speed, power, etc). Watching Alfaro, I wonder if he even sees the spin on the ball at times.
Buying pitchers only works if you can get them on Arrieta deals, the Diamondbacks are going to be eating a lot of bad Grienke seasons. Otherwise your best bet is safety in numbers.
One thing they're doing really well is finding young RPs, Arano, Rios and Ramos, with a bunch more coming up.
If you have a deep bullpen, you only need three solid starters and the rest can be just above replacement level since they only have to go 5 innings.