Nameberry sites the Irish meaning (and Ashlyn), too. Ashley is really trendy, and any "Ash" name (especially a surname) immediately makes me think of it. I believe that when a name isn't well known (even if it's legitimate), but sounds very much like the original overused/trendy/dated name (Ashley), it feels like someone is trying hard to be unique or creative by adding more letters to the original.
Additionally, the "lyn" ending, whether it is spelled lyn, lynn, or lan, is really trendy, lumping the name with other trendy names like Kailyn, Jailyn, Rylan, Dylan, Caitlin/Katelyn/Kaitlynn, Braelyn, etc.
So, with Ashlan, you have the trendy Ash beginning, plus the trendy lan ending (lan may as well be lyn, because it sounds the same), giving you a double whammy.
That's just my take on things! :-)
I have seen Ashlan as a street name, so that's the first thing I think of. It does have an appealing sound but it's likely to cause a lot of confusion with Ashland, which is more common. You have some great names on your list, though.