Here's the thing... The earliest 210s were underpowered and were tested in the field but changes were made and a lot of changes were made to the production run. In early '41 the production was ordered but the handling problems were instantly noticable, so they changed parts of it. Units started receiving airframes in 1942. Production was halted for various logical and political reasons (I won't get into it) but let's just say that by the time the changes to "fix" the 210 were in place it was early 1943. These were basically the Me 210C.
The changes included lengthening the tail, changing the engines to DB605B engines -- which sadly enough the 110 now had at this time so there was little need for the 210C.
The differences between the combat version of the 210, the 210C, and our Me410, are actually rather small. The long and short of it revolves around the different weapons packages you can run in it (many hadn't been developed under the 210C), the 210C retaining the swept wing, and the engines.
The Me410 was really slated to be named the Me210D, but due to the political strife and stigma associated with it, they went with a new model number entirely.
The 210C had DB605Bs, 1475 x 2 = 2950 total HP. 5,440 kg empty weight. Loaded weight 8,200 kg and up.
The 410 had DB603As, 1750 x 2 = 3500 total HP. 6,150 kg empty weight. Loaded weight 10,000 kg and up.
While the 410 had more horsepower, it had a lot more loaded weight as well. However, given the timeline of when the 210C was being made, the time before the Me410 was pushed into combat, and the already-in-existence Bf110G, there's not much of a need for this particular airframe.
It doesn't fill any gaps in the timeline. It wasn't an overly widespread airframe with a significant impact. It didn't bring anything to the table that wasn't already there with other airframes. If the 210 had come out as it should have without all the politics and delays in 1941/1942, it would have been 50mph faster than the contemporary Bf110s. That would have been major. However it say still while trying to fix its problems while other airframes lept forward. The 110 that it would have superceded simply outpaced it in performance.
Look at it this way: The 110G was in service first thing in 1943 using the same DB605 engines that the Me210C would use. The 210C had a top speed at 18,000 feet of 360 mph. Take a look at the 1943 Bf110G as it stacks up to our Me410. So, we have a more representative airframe, used in every front of the war, in numerous roles, and a veritable workhorse, and it already does better than the niche Me210C would.

I list all of this just to illustrate how little difference there was between the Me210C (the primary version) and the Me410A (which we have) and how we already have that role/hole filled with our Bf110G-4 version. However, in an ideal world there would be more variants and versions of more airframes. When we get to that point, I'd love to play around with an Me210. Until then, it's really low on the priority list.