AWith the 16th-level wizard facing you, the EL rises to 17. That's too difficult. Although I have an issue with the "average" party level being 10-12 when one party member is ECL 14.
Maybe you should have talked, but that's not an excuse for using an overly powerful encounter. Mind you, with the power your character had (ECL 14, I believe) I suspect the rest of the party were also using optional rules making them more powerful than they should be. DMs commonly top up encounters by 1-3 or more points if their party seems too powerful. It could just be a miscalculation (and that's a valid excuse).
Springing a boss encounter on the players without some kind of warning is unfair, IMO.
Yes. It's called tactics. That's why enemies often target the wizard first, wall up the cleric with wall of x to keep him from healing the party, "focus fire" on a single party member, etc. It's fair if the encounter is something the party can actually deal with.
That's not vindictive (picking on the same character... that's smart tactics), assuming this was balanced by a saving throw with a reasonable save DC to avoid the Con damage. However, you shouldn't have to face an uber-hard boss encounter after another difficult encounter.
Yes, although that encounter was over-the-top.
A typical encounter is supposed to be easy. Bosses are supposed to be better, however.
Anyway, the DM is supposed to do that. Lure you into overconfidence, watch your defensive strategy, and then shatter it.
There's such a thing as a game that's too hard. I see this frequently in low-level campaigns.