You are describing the compatibility clause as if it's settled that the EUPL simply allows you to convert to a compatible license. The compatibility clause is an unfortunate ambiguity, but it's not the intention of the license authors to lose strong copyleft and SaaS loophole protections this way. See for example here [1] [2] [3].
[1] https://interoperable-europe.ec.europa.eu/collection/eupl/di...
[2] https://interoperable-europe.ec.europa.eu/collection/eupl/ho...
[3] https://news.ycombinator.com/item?id=45422512