Interesting. Perspective is a funny thing. From where I'm sitting, that appears to be what people are insisting they get/be allowed to do. Give me all of the optimization and powergaming abilities I want and "I shouldn't have to" pay anything for it.
And you absolutely can "do melee" with a low to mediocre AC and HP...druids, rangers, thieves and some clerics have been doing it for decades. It may be unwise to go charging in "blades blazing"...but then something like an avenger isn't for doing that. Something like an avenger -whether built off of a paladin or a monk or a rogue- using a little smarts and a bit of stealth, going after one "specific target" at a time, ought to be able to operate just fine in melee...with MAD/not getting the bonuses another "full-classed" archetype would have.
Druids have a HP buffer.
Melee great weapon rangers wear medium armor. Dual weapon ranger don't have MAD.
Rogue sucked at meleeing anything that wasn't weaker than them until 4th and 5th gave them "escape melee" features
Paladins were not given any features to make up for not wearing heavy or medium armor. You can make an avenger with them. However if you make a light armored warrior who uses two handed weapon and divine spells, you will be below the par for the table until you powergame over the table's standards.