Pete, hard question.... As two different level camera's...
The 1200d is a very able camera but it's an entry level camera with limitations to it, it's not long before you get frustrated by the frame rate speed, it gets sluggish very quickly, even with just selecting Jpeg.... The focusing isn't as fast as the 7dmk2, but you don't notice prior to using the 7dmk2 though.... The 7dmk2 is the superior camera out of two, so you're upping you changes of hitting focus and tracking, holding a burst at a good frame rate that increases the percentage of nailing the shot...
But the there are many reasons why I prefer the 7dmk2 for shooting wildlife...
I have mobility issues with my shoulders, and my left shoulder being the worst, can get very sore indeed... So you would think that the lighter the kit the less problems I'd have, but this isn't so...
If you've got an heavy lens on a light camera body, there's no real counter balance to the lens, so you supporting more of the weight of the lens, while with the other hand, trying to pull the body down to counter weight it.. With an heavier body it's easier to counterweight so takes the pressure off the supporting arm....
Also, with the 7dmk2 body being larger than the 1200d, pulling in your elbows against the body, isn't so far to go, it was having to really pull in tight to probably support the 1200d, that put a lot of pressure on my shoulders, causing real discomfort. with the 7dmk2 I don't get the pain level in my left shoulder, nor find after being out for the day, I spend the night with a niggling ache in the shoulder.
But saying that, the 7dmk2 preforms very well with wildlife photography,
But if budget is tight... Then the 1200d will more than able, with some limitations to it....