It's more complicated that that.To use your example, a Level 100 Metwo with Hardy nature and 29 SAtk IV's(and no EV's) has a SAtk of 342. A Level 100 Metwo with Modest nature and 7 SAtk IV's(and no EV's) has a SAtk of 352. So your nature has a far bigger influence on the stat then the IV's. EV's have an even bigger influence so EV>Nature>IV is correct
IVs and EVs both give a 'fixed' stat boost. For IVs, 1 IV is 1 point, and the variation is 31. For EVs, 4 EVs are 1 point, meaning the variation is 63 - ie twice that from IVs. (All this is only for level 100).
Nature, however, is a percentage, and is applied after IVs and EVs. The boosted stat gets boosted 10%, and the dropped stat dropped 10%.
So whether IVs or Nature is more 'important' depends on the base stat. If the actual stat, after EVs with a neutral nature and no IVs, is greater than 310, then the positive nature does more than the 31 IVs. If the actual stat is less then the IVs do more. This corresponds to a base stat of 121.