Here's a glimpse of what's left of that so-called Marxist heritage:
A glimpse is something you see, therefore I take your quotation to be a view, your view no doubt backed up by something other than itself. Yet, you request others qualify their scepticism with evidence, research.
The graphs here give a less clear picture - i.e. it's less clear that "incomes have been falling for years."
Moreover anyone paying attention would have noted that western sanctions have forced a reorientation of the Russian economy into domestic production. This has had many spin-offs including becoming a net food exporter. A wider point must surely be, condemning Russian policy by the measure of domestic disposable income (which rose slightly in 2019 according to https://russiabusinesstoday.com/economy/real-disposable-incomes-in-russia-rise-0-8-in-2019/ )