I agree with you, but Lith is still worth raising an eyebrow. As others have said, this is a nation that turned to Poland in part for survival. It doesn't have the population or other data to back up its 1444 position, really there's no convincing historical reason they should be anywhere near that ballpark, so what is the justification for Lith at 350 development? What is the justification for it at 150 development?
Well, they were able to fight, if not entirely successfully (they lost the wars, though not by that much) 1500s Muscovy, which in game currently sits at a bit over 500 development (including vassals, 357 without). Lithuania at that point is at 335 development, with substantial autonomy issues and half the income that Muscovy has; they are unable to afford their full force limits. Muscovy at that point quite easily trounces Lithuania and can actually take on the full commonwealth. Relative to each other, I think that their developments are in fact pretty fair; they are supposed to be reasonable opponents, with a lot of other factors contributing to Lithuania losing their wars vs Muscovy (though the PLC won vs Russia). Nerfing Lithuania would have to entail a sizable nerf to Muscovy in order to keep the region fairly balanced.
One thing everyone should also note is the autonomy situation in Lithuania at game start. They actually have horde levels of autonomy, with 25% in most provinces (including estates) and 50% or more in plenty more (average autonomy is probably about 30-40%). In addition, they have 4 of their richest provinces with unaccepted cultures AND high autonomy (62% autonomy in their richest province). There is also the religious issues, even with their high tolerance Lithuania has unity issues, even a bit of war exhaustion can push the revolt risk above 0. The end result is that though Lithuania still has reasonably high development, they actually are much weaker than that in reality (and have less options to quickly increase their wealth, unlike many other powers).
Truth be said, if you could direct Lithuania to spam claims on Muscowy it would probably go east

I know I would. Would even choose Exploration after I finally reached Siberia
True, but Poland, when it keeps the union, is the dominating factor in direction. AI Poland tends to go south or west until it forms the Commonwealth, at which point is tends to be a beast. I have seen independent Lithuania's go more into Russia though.