Spear could be much improved by extending its duration to a minute (two minutes with Royal Road duration extension). You have a reasonably good chance that a targeted player will use multiple Job abilities in that timeframe. Why they chose to make this card have a SHORTER duration than the much-easier to use Balance or Arrow, I have no idea. It does make it an easy choice for Royal Road, though!
That change would be hampered by the whole "can only have one card buff active at a time" thing, though.

If they got rid of that silly rule at the same time, then yeah, it might serve more of a purpose.