The argument is that the effect of the invasions on both the Rus and other peoples in regions the Mongols conquered or subjugated might have been hugely beneficial to the ability of Tsars to rule a huge amount of land from St Petersburg afterwards, most of it to the east.
That's is entirely consistent both with it decimating the earlier civilisation across a smaller region centered on Kiev, and with it having a negative impact on economic and cultural growth in that region and surrounding regions which was felt centuries afterward. Especially if you consider Tsarist rule that Mongol invasions arguably paved the way for to be amongst the factors responsible for the relative backwardness of the Russian Empire.
