I mean, I suppose it's probably better to say that it's mostly OK to go 90% of the way, since it's relatively inexpensive to do so for most jobs (i.e., go with an nq that's 2% less effective if it save you 1mil on a piece you'll use for 5 levels... people probably won't be too harsh on you for not having a pair of sniper +1's and a speed belt on your first 75), but if you're not willing to put in the effort you'll likely end up in the Gimp Players thread.
Some jobs are just flat-out more expensive than others to not suck at, e.g.: if you're a WAR with a half-leveled NIN sub in the 60's wearing full AF rocking a lv40 greatsword and nq amemet mantle and balance rings, people are gonna be upset (or at least talk about you in their LS). If you're leveling SAM, then yeah, you're probably gonna need to take the time and save up for some Kote, a Hauby, etc. BRD? COR? RDM even? Yeah, you can probably cheap out a good bit and people won't notice much or care, and it won't have a huge impact on exp/hr.
Of course, if you're pimped out, it sure helps
Having a COR pop off respectable Slug Shots while still getting rolls out efficiently definitely doesn't hurt exp/hr.