While I don't really have any useful opinions on the main point you raised in your post, I can answer this question. 
The answer is yes. A single inheritance clause with a protocol composition is equivalent to multiple inheritance clause entries where each one is a single protocol.
There's also an interesting useless bit of trivia here. Could we hypothetically deprecate the , syntax for writing out multiple inheritance clause entries and always have a single one which might be a protocol composition? The answer is almost, but not quite, unfortunately. The one exception is that enums can declare a RawRepresentable conformance by "inheriting" from their raw type, eg
enum Foo : Int, SomeProtocol {
case a = 1
}
Since Int is neither a protocol nor a class, it cannot appear in a protocol composition, so it would not be valid to write enum Foo : Int & SomeProtocol.