but to know what your rifle can do good ammo is necessary, plinking rounds are good to get down range but I'm from the school of thought that says, have the best ammo to know what I'm doing wrong in my shooting form, or if it's my gun that's not holding true... you need to know the capabilities of your set up.
This.
While expensive match ammo isn't a real necessity, if you're shooting surplus that isn't minute of angle or close to it- you can never know if it's you- or the rifle. For an inexperienced, or "meh" shooter, it's best to have someone that can shoot determine the rifle's capability as best as possible, using some FGMM or Black Hills. Then, you know what the rifle can do- the rest is up to the human behind it.
Other thing is, the OP never told us what rifle he's shooting. Could be, the RIFLE is "meh"- and he's doing everything right.
Without knowing for a fact, that you have an accurate rifle AND ammunition, you have no baseline for evaluation. If a shot prints 2 inches left, you need to know it was YOU, and not the ammunition, or an inaccurate rifle.