On the contrary, the game is realistic in this aspect. Czechia was basically never able to close the borders so tightly you would prevent "all imports". What "closed borders" meant in practice were tens of thousands people crossing the border every day. With prevalence in the rest of the Europe often much higher than 1 in 10k, this means you always have a stream of imports.
Note that some of the borders look like this: https://polar.cz/data/gallery/modules/polar/news/articles/vi... you have a town on both sides, and in normal times, due to Schengen, people are used to work and shop cross-border. ?In such contexts you can prevent most of cross-border travel, but not all of it.
As for the political aspect of the question, ie.: "what options are available to us"...
I regret to be so blunt but in almost every case, when you hear people say that we can't afford eradication and that the best we can do is mitigate, that right there is what I would call serious political bullshit. It's what politicians say when they don't want to make difficult unpopular decisions. Eradication is almost always* the cheaper option.
* (exceptions may apply)
This game has an unrealistic rate of decay when measures are taken. You can take every possible action (full lockdown, throw all the money at the problem) to the max from day 1, and you'll spend the whole game at 10 new cases per day, even after the vaccine rollout. That's just not how things play out.