Mearsheimer's getting a lot of airplay right now, but his analysis is straight out of the 19th century "great game" -- Ukraine is hardly even mentioned. His reasoning is all about the territorial conflicts of the "great powers".
In reality Russia is a small, poor, and mostly irrelevant state, mainly getting airtime because it has nukes. Without the nukes it would be taken as seriously as other countries of its economic clout, like Australia. Which is to say, not taken seriously at all.
Russia provides something like 20% of global wheat supply, something like 15% of global agricultural supplement input, and something like 12.5% of global oil/gas. They also have an enormous intellectual human capital history — the soviet era physicists and mathematicians were definitely peers to their western counterparts, which is to say nothing of their literature. And finally, they have top-tier homegrown armaments in nuclear, submarines, ICBMs, fighter aircraft, and so on.
I think any metric (e.g. GDP) that reduces this multidimensional situation to "mostly irrelevant" is probably saying more about the metric than about the reality on the ground.
They are far far from an imperial power though, and haven’t really been one since the mid sixties, perhaps earlier. They should just face the music as onetime apex predator Britain has. Italians are proud of their Roman forebears but have no pretensions of contemporary imperial greatness. Likewise Turkey.
In reality Russia is a small, poor, and mostly irrelevant state, mainly getting airtime because it has nukes. Without the nukes it would be taken as seriously as other countries of its economic clout, like Australia. Which is to say, not taken seriously at all.