But if the colony is powerful enough to declare war on a "great power" anyway, it shouldn't be a problem.
Well if its powerful to declare war on a great power its hardly a colony is it?
For gooods sake hehehe...
A puppet state could be considered to b on the verge of barbarian state.
And um why?!
We shouldn't immediately percieve to create a narrative with whatever perception we think of for these new diplomatic / vassal options, they are governed really by circumstance. The circumstance is this.
A great power forces a nation to capitulate and or - releases its own territories (ruled directly) into an independent AI colony.
An Imperial power creates a colony in order to harness that lands resources yeah? Ie. The colonisation of North America by the European Dynastic Monarchies etc. The fact these places grew to become so powerful that they demanded independence - resulted noticeably in North America for 'new colonies' and colonies resulting from subjugated peoples (such as India, and other ethnic/cultural peoples' ruled over by the Europeans.)
Would Australia? the British Raj or the Belgian Congo declared war on other nations by themselves? No... because they ARE colonies - and there ruled by viceroys, administered directly.
At the very point where they could declare war or control there own foriegn affairs, they very rapidly ceased to act as colonies.
While a puppet state should certainly not be on the verge of a barbarian state? Like why make that assumption? Puppet states too are an extension of imperialism, which like colonialism sought to harness resources, land etc (with the exception that puppet states) allowed for the extension of prevailing political idelogies and geo-political balances. But any puppet state was useless to its 'imperial' master if it was just crap. So they all tried to make there puppet states decent 'for purpose' so for example, East Germany from the Soviet Union was a great deal more sophisticated than say Mongolia. Likewise with Western puppets (such as Pinochet in South America and so on) that we helped er install in the West.
However quite right, i think the puppet states should have 'considerable' but not ridiculous penalties in the rev / revolt index. Its about striking the right balance.
We know wars were often fought over protectorates/colonies/puppet states etc but its the rare exception to the norm, that these states themselves directly initiated conflicts by themselves to bring great powers to war.