The first reason why I disagree is that multiparty politics gives people choice. Right now people have two choices. Go to Germany and they have six or more. Right now they made the choice to have very few parties, well that's because they have a 5% cut off and two parties got to within 0.3% of that but didn't get seats.
Two choices still exist.
No matter who you vote for, you are deciding for a liberal or conservative coalition. It works that way in Germany too.
The ruling coalition is called the government, while the coalition not in power is known as the opposition. If you refuse to join a coalition, then you get butchered during elections.
In the UK UKIP have risen up, the Lib Dems were in junior govt. In Germany the CDU/CSU and SPD are the main parties but will form coalitions with the FPD or the Greens. This means that people who vote for lower parties may actually get their policies through, meaning more democracy, not less.
Some political parties in coalitions swing, which makes the major parties accountable to
make promises. These are mostly single issue parties.
Those promises are empty though unless there is already majority consolidation, like is already the case in the US two party system.
Often minor parties are irrelevant too, because if their ideas become of any significance, they just become adopted by the primary political factions.
If you ACTUALLY look at politics in other countries, you'll see that where there are more parties, politics is healthier.
The countries you referenced, Germany and the UK, are just as disenfranchised and upset. Both were actually already on the path to implosion before the US 2016 election, and still are.
