There will always be supremely talented players that can jump right from a foreign league into the NHL and see immediate success. There are however others who need a period to adjust and others who never will adjust. We can come up with countless examples of the latter two categories if we want to.
The "ice size" argument for me is really a lot more than simply adapting to the dimensions of a smaller ice surface. It's about adjusting to the pace of the game, both in terms of the physical speed of the players and the time you have to make decisions and to react. Those factors also lead to a more physical game where more effort is required to get to the spots on the ice you want to be and to maintain your position there. Again, for some guys this is no problem, for others it takes some time, and for others still, it's a deal breaker.
Kakko came over and was winded after a 30-second shift and looked like he had bricks in his skates. It's hardly a surprise that he didn't adapt well to the NHL; even if he was playing on smaller surfaces previously, it's all the other things that go along with it that made it a really tough transition for him. Lias Andersson was much the same and he has yet to demonstrate he can play fast enough (again, physically/mentally) to become an NHL regular.
Ice size on its own probably isn't enough to hold a guy back, but the other factors that result from playing on a smaller surface with oh-by-the-way the best players on the planet, for a lot of guys it requires an adjustment period.