I am certain that you're right. When my partner Anne started learning the fiddle she went through a longish phase when she could play the approximate note she was aiming for but not the exact note. During this period I soon learned to accompany her on anglodeon rather than anglo because the accordion reeds were much more forgiving of the slight dissonances than the concertina reeds.
but as you mention about the pokerwork, it may be that the reedier accordion sound is more forgiving to the ear of intervals that are off. we're kind of used to hearing tremelo-tuned accordions anyway, so maybe we're not expecting to hear pure intervals in the first place on them.
On the other hand once she had learned to play in tune then I found that the sound of concertina and fiddle together is really lovely.
How is your Anglodeon, btw? I looked at the layout way back, when you posted it, and thought it will not be really playable, because on the Anglo you can jume from right hand C row to left hand G row, then back to right hand G row for continuous playing, but on the Accordion it will mean jumping an octave. So you can't play across the row, since the adjuscent button on the other row is an octave apart.
Seems like you're doing all right though, so may I ask for a report of your playing style, problems and work arounds? Pure curiousity at this moment, but who knows?