First, tax competition creates its own inefficiencies —- companies locate production in low tax jurisdictions instead of optimal locations given local skills, factor prices, etc.

Second, this argument only makes sense if you think tax competition leads to “innovation” in tax policy, but it’s not clear why that would be the case. Almost any kind of tax structure is jurisdictional and would be undone by zero-sum competition between countries.

Third, would this hurt developing countries? Right now this is a voluntary agreement between developed countries to achieve a common goal, so that complaint isn’t super relevant. Think of multilateral tariff reduction agreements —- it’s often a good idea to unilaterally put up tariffs if everyone else lowers them, which can result in a high-tariff equilibrium even if each player would like lower global tariffs. Multilateral agreements are the way to achieve the collectively desired outcome that can’t be achieved in a decentralized way.

But a global minimum tax could be also be a good idea for lower income countries, if it’s not set too high. Typically the economic incentives are there to locate especially production in the developing world. If all developing countries had the same minimum tax, then companies couldn’t play developing countries off one another to get lower tax. Lower income countries would reap more gains from globalization and have more funds to eg invest in infrastructure and development.