If you don't handload, the 30-30 has a flatter trajectory than traditional factory loads of the 45-70.
I own both, and I think that's probably where you are headed.
I started with the 30-30, and it's been my go to cartridge for many years, for deer, bear, and moose, it's always done the job for me.
When I got the 45-70, I hunted with it heavily. But as I got older, I found that the 30-30, lighter, and handier, was the cartridge I found myself toting around to hunt with when I had a lot of walking to do. For me, that's most of the time.
Now if you are a stand hunter, that only packs his rifle from the truck to the stand every day, weight isn't an issue, in fact, it's an asset, the weight will steady your shot.
The 45-70 is an amazingly versatile cartridge if you handload, but, so is the 30-30.
Both can be shot at full power with home made cast bullets.
You can download them to rabbit/grouse hunting rounds, or use them at full power.
The 45-70 even at Black powder power levels, will take any game on the continent, if you can get over it's rainbow trajectory at those levels.
The 30-30 held the world record for Grizzly for a number of years, that's a good indication of what it can do. But it's decidedly NOT a recommendation to hunt griz with it.
Lots of folks will tell you that the 45-70 at factory levels is no good past a hundred yards or so. Ballistics speaking, looking at the tables, that's roughly true. However, in the real world, those of us who have hunted with it know that it kills out of all proportion to what you read on paper. Mastering the trajectory is the key with the BP power levels.
Brush busting, that's largely BS, everything deflects. Better to focus on having enough killing power left after your bullet is deflected to do the job, if the bullet still connects.
At bush ranges, both will do that.