I do think people were a bit too hard on Lokiare.  It was a legitimate question, assuming it was asking what concepts you can't make with the rules as we have them now.  Of course those things will change once the game is out, let alone once we start getting splat books.
There are things one cannot make at the moment.  That said Lokiare's parting shot really tarnishes what he was presumably trying to say.  Also a number of the concepts that supposedly aren't available actually are if you are willing to multiclass.  And in some cases even without.
The lightly armored/unarmored fighter who wields a big weapon is possible so long as you are willing to multiclass barbarian.  The rage can be ignored, or better yet refluffed as a battle trance, getting into the rhythm of battle, or something similar.  This would require 3 good stats, but a human can have 3 16s if they are willing to tank their mental stats.  And fighter does get the most stat increases.  This means with a single level of barbarian added in, and having the three physical stats at 16, the "fighter" can have an AC of 16.  Add a second level of barbarian and they can get advantage on their attacks pretty much at will.  Multiclassing barbarian is a small price to pay to be able to go without armor and still wield a big weapon.
As for the Defender Wizard.  Well Mages still get buff spells that can help them in combat, though most of those will be Concentration so they can't cast a bunch of them on themselves, and the new suggestion of taking damage ends concentration may ruin that even further.  But beyond that there are the Enchanter Wizard option that is potentially broken, and one can be a dwarf and at 4th grab the feat to wear heavy armor.  As an added bonus you can focus on upping Con and Int and have more HP as well as some damage resistance equal to Con mod.  Makes a pretty good tank wizard after all.  The Enchanter Mage 2nd level feature is so crazy that some melee characters, especially fighters, might take 2 levels just for that.