Proportional representation would not make a difference in a system with an executive elected by general vote. Political grid lock is just as likely, leading larger parties to form alliances with smaller, but more extreme parties. This leads to what we see in Israel, where large parties form an alliance with a small conservative religious party who in return demands traffic lights be turned off on the Sabbath.
As if that is typical of a parliamentary system with proportional representation.
Let's look at measurements of strength of democracy like
I found this combined ordering:
1 Finland, 2 Norway, 3 New Zealand, 4 Sweden, 5 Iceland, 6 Denmark, 7 Canada, 8 Ireland, 9 Switzerland, 10 Netherlands, 11 Australia, 12 Uruguay, 13 Luxembourg, 14 Germany, 15 Japan, 16 Austria, 17 Portugal, 18 Slovenia, 19 Belgium, 20 Estonia, 21 France, 22 South Korea, 23 Taiwan, 24 United Kingdom, 25 Costa Rica, 26 Mauritius, 27 Chile, 28 Czech Republic, 29 Italy, 30 Malta, 31 Israel, 32 Lithuania, 33 Slovakia, 34 Spain, 35 Cape Verde, 36 Cyprus, 37 Latvia, 38 United States, 39 Barbados, 40 Greece, 41 Panama, 42 Poland, 43 Argentina, 44 Croatia, 45 Romania, 46 Mongolia, 47 Trinidad and Tobago, 48 Botswana, 49 Bahamas, 50 Bulgaria, 51 Jamaica, 52 Malaysia, 53 Suriname, 54 Hungary, 55 Namibia, 56 South Africa, 57 Ghana, 58 Grenada, 59 Antigua and Barbuda, 60 Brazil, 61 Dominican Republic, 62 Guyana, 63 East Timor, 64 Singapore, 65 Albania, 66 North Macedonia, 67 India, 68 Peru, 69 Seychelles, 70 Indonesia, 71 Montenegro, 72 Serbia, 73 Belize, 74 Moldova, 75 Tunisia, 76 Paraguay, 77 Ecuador, 78 Colombia, 79 Lesotho, 80 El Salvador, 81 Samoa, 82 Bhutan, 83 Fiji, 84 Senegal, 85 Papua New Guinea, 86 Ukraine, 87 Mexico, 88 Malawi, 89 Thailand, 90 Bolivia, 91 Armenia, 92 Benin, 93 Georgia, 94 Sri Lanka, 95 Philippines, 96 Madagascar, 97 Bosnia and Herzegovina, 98 Guatemala, 99 Liberia, 100 São Tomé and Príncipe, 101 Honduras, 102 Kuwait, 103 Morocco, 104 Sierra Leone, 105 Zambia, 106 Nepal, 107 Gambia, 108 Kenya, 109 Tanzania, 110 Bangladesh, 111 Ivory Coast, 112 Qatar, 113 Turkey, 114 Burkina Faso, 115 Nigeria, 116 Pakistan, 117 Algeria, 118 Mauritania, 119 Jordan, 120 Lebanon, 121 Uganda, 122 Comoros, 123 Kyrgyzstan, 124 Oman, 125 Mozambique, 126 Kazakhstan, 127 Niger, 128 Gabon, 129 Maldives, 130 Iraq, 131 Angola, 132 Togo, 133 Haiti, 134 Mali, 135 United Arab Emirates, 136 Russia, 137 Solomon Islands, 138 Vietnam, 139 Guinea-Bissau, 140 Nicaragua, 141 Eswatini, 142 Cambodia, 143 Rwanda, 144 Brunei, 145 Ethiopia, 146 Cuba, 147 Egypt, 148 Djibouti, 149 Zimbabwe, 150 Bahrain, 151 Belarus, 152 Palestine, 153 Azerbaijan, 154 Cameroon, 155 Guinea, 156 China, 157 Uzbekistan, 158 Saudi Arabia, 159 Iran, 160 Sudan, 161 Burundi, 162 Venezuela, 163 Laos, 164 Tajikistan, 165 Libya, 166 Equatorial Guinea, 167 Turkmenistan, 168 Chad, 169 Eritrea, 170 Myanmar, 171 Afghanistan, 172 North Korea, 173 Yemen, 174 Andorra, 175 Central African Republic, 176 Dominica, 177 Congo, 178 Kiribati, 179 Syria, 180 Marshall Islands, 181 San Marino, 182 Tuvalu, 183 Micronesia, 184 Palau, 185 DR Congo, 186 Saint Lucia, 187 Saint Vincent and the Grenadines, 188 Liechtenstein, 189 F.S. Micronesia, 190 Saint Kitts and Nevis, 191 Somalia, 192 South Sudan, 193 Hong Kong, 194 Monaco, 195 Republic of the Congo, 196 Vanuatu, 197 Democratic Republic of the Congo, 198 Tonga, 199 Nauru, 200 Kosovo
Most of the top ones use parliamentary systems. So if parliamentary systems are so debilitating, then why has that not been very evident?