Theories of value are untestable, since value isn't price. The LTV can only really be argued to be wrong on philosophical and theoretical grounds, not on empirical grounds. This is because market prices are not necessarily the same as values. There are however plenty of arguments outside the empirical realm against it.
If you want a testable theory from Marxism there really only are two - the aggregate rate of profit to capital will go down in the very long term, there will be endogenous economic crises due to lack of demand/too much supply in aggregate. The rest are unfalsifiable as far as I'm aware. The issue is that both of these predictions seem to be correct so far - P/E ratios are going up and we have now had plenty more evidence that crises due to mismatch between demand and supply are inherent to capitalism.
However, it's still not a great tool at actually predicting the world, because the vast majority of predictions are unfalsifiable. But I agree with you that most of economics is moreso ideology.
If you want a testable theory from Marxism there really only are two - the aggregate rate of profit to capital will go down in the very long term, there will be endogenous economic crises due to lack of demand/too much supply in aggregate. The rest are unfalsifiable as far as I'm aware. The issue is that both of these predictions seem to be correct so far - P/E ratios are going up and we have now had plenty more evidence that crises due to mismatch between demand and supply are inherent to capitalism.
However, it's still not a great tool at actually predicting the world, because the vast majority of predictions are unfalsifiable. But I agree with you that most of economics is moreso ideology.