The key problem with Poland losing Latin tech in the Union of Lublin event, is the fact that they have no chance to fight the change, also, there wasn't a major issue with the Union that could cause a slow degeneration of the armed forces. This is why I choose the "Struggle for Royal Power" event in 1607. This was a turning point, where the nobility would take whatever remained of the monarch's power, and pursue their own goals, which centered more around colonization of the vast expanses than trade in the baltic regions, for example. In that event, the third option, "Wage a War of Extermination Against the Nobility", is just what the monarch probably needed to do at the time to finally force some centralization into the Commonwealth and decrease the power of the aristocrats. And don't worry, Poland pays for choosing this option, +5 RR for 20 years is nothing to laugh at, if Poland doesen't choose this option, she drops to Orthodox. Now during this period, a determined enemy could probably strip some lands from her, giving 1607 a balancing component as well.
While the events are bad, espeically in stripping tax value away from her, she can still I believe pretty powerful if she can just stay on tech parity with the best of Europe. She isn't lacking completely in resources, having a number 3 cloth provinces and 3 iron provinces, as well as a naval supplies province if I remember correctly, which gives her a chance for some nice industrialization as well, which Poland historically was in the middle of prior to the partitions. I don't think Poland was ever "not an innovative" state, as they kept up with trading practices, military theory and implementation.
I believe Poland should have Latin techgroup for both historical and gamebalance issues. A Poland with Latin tech, if he fights the nobility which can be trying SP, would be murderous MP, however if he succeeds, there is no reason whatsoever why he can't remain one of the most powerful in Europe. The true question is, can he survive the struggle as well as exterior threat? Suddenly, with the Latin tech change, I think we'll start seeing Poland not needing to make a ton of silly arrangements just to survive, but actually have a true chance of viability by herself. It'll be a fight, but at least it will be possible, and it should be possible.