Goverment size depends on several factors, not just the percentage of GDP it consumes. Economies with qualified human capital and technological advance will be able to sustain the government's siphoning of funds. The specific political institutions, such as democracy or dictatorship, don't determine size of government. It's indicative of government size but not conclusive.
Governments are only institutions that capitalize on the monopolization of force and everything that the government has was taken from producers and workers.1 Of course government size determines economic conditions because if governments take more through taxes or inflate the money supply it profits on everyone's lose.2 Every country's economic-government relationship is highly relative which makes model building difficult. If an economy is strong and has qualified human capital it'll persevere longer and could maintain growth. Plus, governments manipulate employment rates and economic growth figures to keep the populace pacified.3
(see quote for ref. ^^^)
1. Marx would likely disagree
2. Are you suggesting that taxes should be interpreted as losses? That the government/populace relationship is strictly parasitic, and tax money could be tossed in a bonfire, as far as economy is concerned?
3. Could you suggest an alternative? A way to collect & interpret such data you feel would be provably more descriptive or factual?
1. Yeah, but a lot of Marxist theory wasn't necessarily correct. Marx was right that the aristocracy was being replaced by industry. I think he was also right about his concept of ideology, that being certain classes determine what others think to exploit them. But Marx's solution was to inflate a central organization that redistributes profits from industry which is a phase of "brute communism". Marx said after "brute communism" there would be "absolute communism" which would consist of man as free from factory work and able to spend all his time pursuing his creative interests. The redistributing organization makes it's own ideology though, so his solution doesn't work. His labor theory of value in
Das Kapital has been replaced by laws of scarcity in economics.
I pointed out that governments are not unique in abuse and concentration of power, making the first sentence meaningless. Historically, the workings of large corporations are similar to governments, and their use of power is also analogous -- from arguably evil (use of Pinkertons as private militias, company towns with usurious "company stores" and corporate-issued private currencies), to arguably socialistic and socially beneficial (Henry Ford's use of subsidized housing, child and medical care for his workers).
2. A lot of the government/populace relationship is parasitic. Every single cent that government takes in taxes originates somehow from people that actually make some good, or service the people that produce things. There is however problems with a lack of uniform law systems proposed by some anarchists, because if law isn't generally codified, personal protection agencies could get into a lot of conflict.
In that case the relationship between the brain and the stomach is also parasitic -- the brain produces nothing, relying on the stomach for its nourishment. Seeing the government as a parasitic entity is myopic, the dichotomy between it and society is false.
3. I think it would take a lot of studying to do that. Every government/economic relationship is different. It depends on GDP, private vs. public sector employment, the central bank's monetary policy and all the government interventions.
In other words, no?