A good target for regulation of those clouds would be the inflated traffic pricing.

Either by a simple price limit on ordinary egress (e.g. max 1 EUR / TB to European providers which don't charge for peering/traffic), or by requiring them to peer at-cost with others and allowing the customers to choose such a peering for egress.

The current traffic pricing is extremely high, and makes it difficult to split your cloud installation between multiple providers.

Traffic pricing has to be understood as being, at least in part, a control against free-riding on the provider's networking architecture. The Data Act already gives EU customers a right to egress their data to another provider at cost, which all major cloud providers have implemented. But that doesn't (and shouldn't) mean that they have to give you a marginal-cost-only CDN.