Maybe the OP is just expecting too much from his companions. If you're trying to take on a WB alone with a companion that's on you.
It can be done.
With my pet sorc, I have to trigger the matriarch's heal to keep Bastian up, but he keeps the boss off me so I can do the damage.
With my stam sorc, Mirri chips in with some heals and a bit of damage. In this case it's not a big difference from soloing, but it's nice not to have to do as many self-heals.
Gotta disagree, I love the companion system. I set Mirri up as a Tank and my friend set Bastion up as a healer so we can run dungeons at our own pace without worrying about randoms spoiling the fun.
Sure they aren't perfect but they do the job good enough for most Normal dungeons.
Companion is extremely useless. I want to use second my character as my companion.
I could not disagree more.
My Bastian is fully maximized in multiple skill lines and favor. I've got a bound key for his attacks, which is none but an additional tool in my box that gets used a lot. Moreover, when timed right we can one-shot overland mobs. Together we burn through Delves, Public Dungeons, and very many of the World Bosses. Now, I know most of you studly players do all that by facerolling your keyboards, but since I'm a totally suck player because of physical handicaps, I certainly love me some Bastian.
As for cloning our alts as companions, that sounds a lot like the old timey GW. I'd be okay with that, but -- umm -- I don't see it the way you envision. If it ever happened, the clone would get nerfed into oblivion in order to appease the ubiquitous "this content is too easy" crowd. I also think allowing that degree of customization per player (read: multiple alts with divergent appearances) would overload the already struggling servers.