If a rogue does 70 damage regularly... if 140-210 is max hp, then an average party of 5 will averagely kill anything.
If you want your campaign ender dragon or whatever to last 3 rounds, you'd be looking at about... 630 hp - 3/5 of PCs effective per round for 3 rounds.
In DDN terms that would be a creature vastly above maximum level. Effectively a solo in all but name (unless epic levels are uncapped, in which case it eventually will be a standard mob).
What I was talking about was (in 4e terms) a standard level 20 creature (if the assumed cap is level 20) or level 30 (if the cap is 30) that can be expected to be encountered in a group.
Also, keep in mind that I postulated that because a rogue is a striker, he can kill things in 2/3 the time that a non-striker can. So, whereas a rogue would dish out 70 dpr, a non-striker would deal only about 47 dpr. As such, if the dragon is calibrated to last for 3 rounds you're looking at 705 hp, or 423 hp if the dragon is assumed to keep two PCs out of the fight every round. I don't include the striker's increased damage in that because to do so is to negate the striker's advantage.
The reason I chose a standard mob, rather than a solo-equivalent, was because based on my readings on ENWorld, a lot of those who are against high hp creatures don't have an issue with it if it's the exception rather than the rule (such as for an endgame boss fight).
At the end of a 3.5 campaign, we fought a ten thousand hp monstrosity. The battle took hours and was extremely epic. That said, it isn't something I'd want to see very often, despite that I'm someone who doesn't mind inflated hp (provided they serve a purpose).