I do understand that the teaching in parables is more or less part of the definition of "the messianic secret," or some of the data which the hypothesis sense of the term aspires to explain. This post is not "rebuttal."This automatically leads to Jesus teachings in parables.
Another view of what's on the page, however, possibly complementary rather than competitive, is that Jesus, like other teachers, improves with experience. It follows, then, that early in his teaching career (= here in chapter 4) he can only be less than a perfect teacher (else improvement is logically impossible).
In the boxed 4:10-13, he makes a rookie teaching mistake: his students ask him a question, and he berates them for doing so. This will have consequences: at 4:41, after the calming of the storm, with Jesus right there with them, they ask one another "Who is this?" Why don't they ask Jesus? Because Jesus doesn't take student questions gracefully competently?
There will be further instances of the disciples not asking Jesus questions depite his being physically available to them. There's after the transfiguration. There's when he warns them about the leaven of the Pharisees - OK it's funny that they come up with the interpretation that he's saying they need more bread, but then he goes on about seven of this and twelve of that, berates them for not understanding that, and they still don't ask him "What's up with this seven and twelve business?"
It is also interesting, I think, what it is that neither the disciples nor people outside are undertanding in the metaparable (a teaching about teaching) of the sower. I think the overall message is close to transparent: teaching an open population (as opposed to an elite in-group) will have varying degrees of success in reaching individual listeners ranging from outright failure of connection (the seed on the road) to outright success (the seed on good ground), with partial successes of different kinds in between. Yes, that much is consistent with experience. (In American sports metaphor: you win some, you lose some, and some get rained out.)
But Jesus demands more. The partial successes are to be mapped one-to-one with specific failure modes. Rocky soil means initial favorable reception but falling away under oppression or persecution. Among thorns means being distracted by earthly cares.
Really, Jesus? Assuming we or the disciples guess which two of boundlessly many failure modes you might have had in mind, why wouldn't thorns be a peachy metaphor for being overcome by oppression and rocky soil for being distracted?
(Secondarily, this also goes to the chestnut that Mark depicts the disciples as mental defectives. Umm ... Jesus picked 'em and Jesus taught 'em - maybe the teacher bears some responsibility for disappointing educational outcomes. Maybe Mark is not above being candid about that. But that's a different thread.)