I think that similar "kingmaking" problems can exist in non-PR systems, but the effect is obscured by how unrepresentative the parties are.

For example, instead of a small party forcing one unpopular policy on a coalition, you end up with a single large party that only 25% of the population voted for, running the government without any accountability (because of "safe" gerrymandered seats).

Moreover, these large parties usually contain multiple competing wings, and so are effectively coalitions themselves, except their "coalition agreements" are done behind the scenes, and then internal party discipline mechanisms are used to force all the politicians in that party to follow the party line, even if that party line is set by a minority of a minority.

The Greens actually had little parliamentary influence then: the CDU could have counted on the support of their coalition partners, the pro-nuclear FDP, at the time. Merkel went with massive anti-nuclear sentiment post-Fukushima to pass legislation with over 80% Bundestag support to phase out nuclear power.

It depends on the voting system. Some methods like Proportional Approval Voting are less prone to this kind of gaming in PR/MMD settings: https://electionscience.org/problem-solution/