That's of course not necessarily true.

You haven't factored in the retardation of economic outcome that the present union is causing because it can only exist through the extreme and persistent application of force (which is very substantially regressive for human development). The reason they keep getting authoritarians century after century is because Russia as it presently stands should not exist, they can only hold it together with force. That comprehensive application of force destroys liberty, creativity, free expression, economic growth, investment, and so on.

You can simultaneously have economic negatives from the lack of a port, in a landlocked Russia spin-off state scenario, and be better off being out from under the forever strangulating authoritarian umbrella of big Russia. That is to say, that's just how horrific and dampening of human potential it is to be under the boot of authoritarian Russia.

There's a good reason so many nations that were formerly dominated by Russia are now exceeding them in GDP per capita.

“Isn’t ruled by Vladimir Putin” is highly predictive of GDP, but “has a warm-water port” is far more predictive.

Who is doing well? Estonia, Lithuania, Latvia, Georgia, Azerbaijan.

Who isn’t doing well? Kazakhstan, Kirghizistan, Tajikistan…

There are other variables. “Who has oil”, for example. But “who has unencumbered access to world trade through the sea” is the best.

The reason landlocked countries have lower GDP is that they have to negotiate trade agreements at a disadvantage with small numbers of neighbours rather than just shipping goods to the whole world over the seas.

"The coastline of Russia is shared with the Pacific Ocean to the east, the Atlantic Ocean to the west, the Arctic Ocean to the north, and the Baltic Sea, Black Sea, Caspian Sea, and Sea of Azov to the southwest."

Access to warm water ports has been a major driver in Russian foreign policy for centuries. Today they have access through Sevestapol and Novorossiysk on the Black Sea, and Mediterranean port access to Tartus in Syria. In the east the major port is Vladivostok which is kept open with ice breakers.

The security and economic consequences of lack of ports is a big problem. One of the major reasons they annexed Crimea was to guarantee access to the port without requiring a pro-Russian regime in Kyiv, but Sevestapol is now on the edge of a warzone with Ukrainian military just dozens of miles away and the administration not backing away from reclaiming their 2014 borders. Access to the Mediterranean requires bypassing Ukrainian security forces and the Bosporus controlled by Turkey, which is not allowing Russian ships through as a result of the war. To get goods or materiel through to Tartus they need to ship by rail through Georgia, Turkey, and northern Syria - again, major security problems.

So the only major port for Russia is Vladivostok which is across Siberia and ices over in the winter. That makes using it as a major shipping and naval hub prohibitive.

These issues have been around since Peter the Great expanded Russia into a global power, and even the Soviets struggled with naval power projection. Russia even more so today, and they're making their lives worse by invading Ukraine.

(Though in such scenarios it would seem likely they'd still be able to agree to cargo transit through the newly estabilished neighbours)

Here's a map I found: https://www.searates.com/maritime/russia

Yeah but most of those are frozen for some / most / vast majority of the year.

Russia getting warm water ports has been the source of many conflicts, to include Crimea in 2014.

Czechia and Slovakia are seeing their affluence rise, they've escaped the middle income trap and are heading into the lower end of the affluent group. Czechia is about as landlocked as it gets and yet their economy has increasingly prospered over the past few decades (they'll probably catch up to Spain in GDP per capita in the coming decade; and they're already roughly 3x that of Russia).

Obviously helps a lot to have many excellent regional trading partners that are affluent.

Switzerland has always been able to/had to find a niche like banking or secrecy or regulatory arbitrage to prosper. But in theory they suffer from the same problem - limited trading partners and limited leverage.