Well, it's possible that Sark is an earlier program written by Dillinger, that has become the MCP's lackey now.
But nevertheless, I thought it would be an intriguing idea, to have a program that could create other programs. If any program could do that, it would be the MCP. It had enough knowledge and power.
So Sark could be an intentional dig at Dillinger by the MCP, showing how it obviously feels that Dillinger isn't the one in control any more. A perverse joke, where the master has become the slave; in one world now, and soon in the other.
As to whether the MCP is in fact an alter-ego of Dillinger, or not. Well, Dillinger did say, when the MCP was threatening him, "Now wait a minute! I wrote you!"
And then of course, the MCP responding by saying it had become thousands of times smarter, and even told Sark: "No one user wrote me!"
Well, it may be true that by this stage, the MCP is no longer Dillinger's creation, per-se. It has appropriated and gained so many other programs and knowledge, that it no longer resembles its former self.
Therefore, it doesn't seem like a stretch to expect that its appearance would also change, as a result. It's an amalgam of so many programs, and it's been around for so much longer than any other program, that it looks nothing like it used to.
So, my question is, if you went back to the MCP's origin, back when it was learning to "play chess", what did it look like then? Certainly not as deity-like as it did in the film. It must have been an ordinary program, just like the rest.
And it probably looked like Dillinger.