I'll agree that the 6.5 is very versatile, I wouldn't say it's a bad cartridge for large game, but youre limited to the heaviest bullets for the higher SD to break through those heavy bones and shot placement will be more important than ever.
Also a 45-70 can be loaded from birdshot up to 630 grain round nose slugs. Yes they go that heavy. You can have a subsonic round with over 1200ft/lbs of energy. Pretty impressive, or you could load it "hot" and push over elephants.
I wasn't insinuating that you couldn't take larger game with a 6.5, it's been done for decades in northern europe/scandinavia. I've read several threads about Eskimos and Inuits hunting polar bear with 223, wyoming ranchers killing elk with 243s, F&G killing problem grizzlies with 40 S&W and seen countless medium game animals killed with 22lr(not by me, I'm not that good). anything can be used for hunting as long as you know how to use it properly and I would not doubt for a minute that a 140gr 6.5 bullet could kill anything in the US as long as you know how to use it, I was just saying that unless you are a skilled hunter it may not be the perfect rifle for the job if you need to get at larger animals like moose, elk, or grizzlies.
as for 630GR slugs I would hate to see what one of those things could do