How is it a "dumb expansionist plan" to take historic Rus lands,
Becasue those are not your lands nor your people. At the very least those are Ortodox people who don't want to be a part of Moscow.
Look at Lithuania today.
Lithunia toady is not the Grand Dutchy of Lithunia they would need Belorus as well. The most of all they are reasult of the modern 19th century precess of nation forming where every nation supposed have a state.
Here it is in the nutshell what went wrong:
They are not Lithunians their are Samogitians.
They wanted a nation state but claimed Wilno with lands where people considered themsleves Polish in 90%.
It supposed to be a historical claim - Grand Dutchy and all but at the same time they didn't claim Belrus as well. So they claims to Wilno are based on their political bias. They are a lot like Moscow. lol!
such idiots deserves to run a territory that includes Belarus, Ukraine and most of Western Russia?
Today? Nope. Today we have Belorusan to run Belorusan, Ukrainians to run Ukrainie, ah Belorusans want their land back - Smoleńsk and all.
Historically those all people were happy to be part of Rzeczpospolita and not some Moscow backwater.
In the war with your Ivan in 1580' he wrote to our King Stefan - asking/accusing him of using magic therefor a faul play. Due to use of mortars and other implements of war Moscow was not familiar with.