Did I mix up the quotes? I thought it was you who brought up the AC chart for armor?
I brought up the AC chart for armor to illustrate that all armors provide a numeric AC value (e.g. 11 for leather) to which the DEX modifier is added.
I was saying that, likewise, barkskin could be interpreted as written, to provide a minimum AC value that replaces the armor's AC value. The final AC would then be modified by DEX bonuses, shields and other modifiers.
To me, the barkskin spell is unclear. There are however, contrarily to what is being conveyed by most people here, two ways to reasonably interpret the text. One makes little sense (everybody agrees on that), and the other makes sense.
To rephrase what I was saying, people that support the "AC = 16 minimun including all modifiers" position take the position that the "AC" in the barkskin spell descripition, means "AC including all modifiers". What I'm saying is that:
1) in the armor chart, there is a numerica value for AC than will later be modified by DEX modifiers, shields and other modifiers such as cover.
2) the text of the barkskin spell specifically mentions that the mimimum AC value will be 16
regardless of what type of armor the target is wearing. The text makes no reference to "regardless of shields, DEX mods, cover or other modifiers".
To me, the specific including of armor only in (2) and the exclusion of all other bonuses, then points towards interpretating the AC in the barkskin spell description in the way I mention in (1).
This is what I mean when I say that there is a reasonable interpretation for barkskin to provide a bonus like armor would.
However, since barkskin is not armor, and nothing in the spell says it is, there is no reason to provide any penalty (speed or ability checks) to barkskin.