All Apple should be allowed to do is what they sell to the public to that they do with the App Store: Review apps to make sure there is no malicious code in them and make sure they follow reasonable rules( no data mining, trying to hide access to the camera, etc etc) and take a reasonable cut for the infrastructure they setup.
What Apple has been doing is doing what Google did with Chrome, they see what features are popular in the apps, they incorporate them into the OS itself, change the rules a bit, and now the competing apps are removed for "rule violations".
If Apple allowed apps that competed against their own built in features and did more what they sell the public on what they do, didn't cut Amazon, etc special lower cuts, and other unsavory actions, the case would be considerably weaker. But the House report does have a decent case against Apple that they misused their position.
Note: I don't support Epic in their fight against Apple at the same time.