I think it's clear that players like Fetisov, Makarov, and even Balderis and others could have been big NHL stars in their primes. But to start speculating about an alternate reality is kind of pointless -- I mean, it's exactly the same as saying, "if so-and-so had played on this team instead of that team, he could have scored 150 points a year". Yes, anything is possible when we're wildly speculating.
Take Makarov. Was he a world-elite level talent from around 1978 to 1990? Yes, absolutely. But speculating that he could challenge Gretzky in 1981 in scoring is based on... what, exactly?
At age 31, in his first NHL season, he scored an impressive 86 points. He was fourth in scoring on the League's #1 highest scoring team. Now, we can look at this two ways: (1), He was a first-year player, probably not given much 1st unit PP time, and he had to make his way into the Flames' pecking order. Thus, at the same age, if he'd already been an established player and was already familiar with the NHL and the system, etc., it's certainly based on realistic evidence to say he could have scored more points than that -- maybe, I dunno, 100 or 110 or something, at age 31? But we can also realistically say: (2) If he had started with a lower-scoring team with less talent (almost any team except Calgary in 1989), he might have scored less.
Now, we know Gretzky at age 30 scored at a 167-point pace, on a similar level offensive club (1991 Kings).
After Makarov was a bit more established, he scored 70 points in 68 games, at age 33, with a pretty-bad Flames' team (nevertheless, one that could score). That's an 84-point pace. At the same age, on a very similar offensive caliber-team (the '94 Kings, which also sucked), Gretzky scored at a 132-point pace.
So, we can always speculate about what could have been. Maybe Makarov learns English at night in his spare time during 1975-1978, comes to North America somehow in 1978-79, spends a year in the WHA, then joins the Bruins and scores 165 points in 1980-81. I mean, I can't say it's impossible. But I can also say there's absolutely no evidence suggesting it's realistic.
There are just too many intangibles related to playing in certain Leagues in certain styles, with certain teams. Maybe Makarov isn't the kind of player who'd excel in the long-season, physical grind of the 1970s/80s NHL (in 1989-90 he scored 21 points in October, and then scored at a 78-point pace the rest of the season). Or maybe he is. Who knows?
Look at Peter Šťastný. Yeah, the Nords knew he and his brothers were big talents on Slovan Bratislava, but who expected that he'd step into the NHL and immediately be a 130-point scorer for several years? Some guys just suit some environments and some don't.