As a Finnish speaker, I don't get that feeling with Estonian. The written form is different enough to warrant a deeper look before I start whining about how annoying I find language studies in general.
Granted, I'm also super lazy, but Finnish and Estonian should be close enough to just have some threshold to get over until it's pretty smooth, I guess?
Fwiw, I'm native in Swedish, but I speak and write Finnish daily.
To go on about my earlier comparison, I can really visit the site for a Danish or Norwegian Bokmål newspaper like Politiken ( https://politiken.dk ) or Verdens Gang ( https://www.vg.no/ ) and start reading with a feeling of just moderate confusion. Academic text would require some extra effort. The "voice in my head" or mode of reading doesn't really even change, because I've never attempted to communicate in either Danish or Norwegian per se.
For Estonian Postimees (https://www.postimees.ee ) I'm stuck pretty much immediately. I can pick up words and some context, but that's it.
At my first job, at an internal IT Service Desk for a certain Nordic energy company, I dealt with Norwegians and Danes. But it was a business context where everyone just seemed to agree to just make a polite effort at having a maybe slightly "clear in a Swedish way" common Scandinavians language, because switching to English would feel a little silly. I guess some of the older dudes working in the field somewhere in Norway might not have spoken English.
Many words in standard Estonian do have true cognates in Finnish, but the Finnish counterparts have a slightly different or more specific meaning, or are nonstandard or colloquial. A typical example would be maja which in Estonian means "house" or "building" but in Finnish has the more specific meaning of "hut" or "cabin"—a dwelling more rudimentary and temporary in nature.
EE: ära surra (to die) - FI: surra (to mourn)
EE: vaim (ghost) - FI: vaimo (wife)
EE: kannatus (suffering) - FI: kannatus (support)
EE: pulm (wedding) - FI: pulma (difficult problem?, puzzle)
But anyway, there we probably have it, your vacations as a child. No lifehacks can beat exposure to language at a young age, I guess. SAD.
Waiting for the day when some drug can trick the brain into some semblance of a kid's language learning skills.
My Finnish is poor enough that I didn't recognize any of the alleged similiarities.
As a (non-fluent) Spanish speaker I get a similar experience hearing Portuguese, the words sound similar but different and the speaker sounds slightly drunk.
Greek sounds very close to Spanish but none of the words mean anything, it's really weird :)
I don't hear Greek that often, so the suggestion also struck me as weird. Some analysis: https://www.youtube.com/watch?v=LPMqoHPJzac
I have a Swedish friend who described Danish speakers as sounding "like they're speaking Swedish with rocks in their mouths"
Anyway, add the Vigesimal system for numbers above 49 and you're really off to the races https://www.kbh-sprogcenter.dk/en/blog/learn-danish-numbers/
For the sake of hilarity, let's add that Icelandic people are forced to study Danish in school Because Reasons. Icelandic is not mutually intelligible with the major Scandinavian languages, even in written form. The argument for studying Danish is of course that everyone benefits from Nordic countries sticking together.
But Danish is the most cumbersome way to get some of that benefit of a common language.
Some Icelandic professor character actually recently dropped a hot take, suggesting that Icelandic schools could switch to teach some form of Finland Swedish, because it'd be remarkably easy for Icelandic speakers to pronounce and probably the easiest option for most people in the Nordics to grasp relative to effort. https://translate.google.com/translate?hl=en&sl=auto&tl=en&u...
Being a Swedish speaker from Helsinki, Finland, I kind of don't like the nasality of my own dialect. I'd prefer to listen to dialects from the Swedish west coast around Gothernburg all day, because those are very soft sounding. But the suggestion likely makes some sense. Formal/common institutional spoken Finland Swedish is indeed overly articulated and devoid of slang.
Informal Finland Swedish tends to be hyperlocal and may carry loan words from Finnish, which is a non-starter in the other Nordic countries, and very much frowned upon by Swedish schools in Finland.