I love my MkV! It is MY favorite amp for my needs to date and I have owned it since its release four years ago. I also own a MkIV and many other Mesa Boogie amps which I also really enjoy, just not as much as my MkV overall.
1. Is it a Mark? Hell yes, but one with a lot more flexibility in all 3 channels IMO.
2. Do all modes offered in the MkV (MkI, IIc+, MkIV, etc.) sound exactly like their true counterparts? NO, but each mode of all channels of the V can be set to sound terrific IMO. The modes and sounds offered in Ch1 & 2 alone are better than those of previous Marks (at least my MkIV)....by far. The modes and sounds offered in Ch3 of the MkV sound great and work very well for me, but are NOT exact duplicates of the IIC+ or MkIV. I don't find this to be a problem, but that is just me.
3. Is it the "Swiss Army Knife" of the Mark Series....capable of all sounds, but master of none? Some think so, but not me. In fact, I feel that some of the best "Mark" sounds reside in the MkV.....especially in Ch1 and Ch2! Some people really don't like the MkV sounds offered in Ch3 which is fine and I understand they don't sound exactly like their IIC+ or MkIV counterparts. However, personally, I am able to dial in great sounds in Ch3 of the MkV for my taste. To each their own.
I have never played through a Uberschall TJ....so really can't provide any useful info regarding that amp.
The MkV is very capable of being set to sound great for all styles of music IMO....and yes, Metal if that is what one desires. When rehearsing or playing live, I set my MkV channels for a nice clean, crunch and high gain lead sounds which work great for all styles of music for me...Rock, Blues, Country, Pop, etc...
Personally, I don't play metal at all....
My advice is to spend some time playing through the MkV if possible and form your own opinion.
Best of luck whatever you decide!