Artie's performances have been good. Servicable. As i said upthread i see a lot of potential...but that's all i've seen: potential. Good (i could even go so far as saying "great" as far as recasts go)...but Steve was "superior" and even though one wouldn't expect a recast to also be "superior" at first, i would at the very least expect "excellent'.
My thoughts on the quality of Kermit's performances - like my opinions on everything else Muppet-related (people pretty much know by now that i'm very honest about praising something that deserves it but also don't hold back about what i find lacking) isn't going to change based on the reason why it's happening. I can judge the quality of a performance regardless of how come a change happened (but i will also be honest that i think there are a number of fans whose opinions are a bit colored by their feelings...even if it's purely subconscious). But what i was saying earlier is that by knowing why, that allows us to accept the change. If we know that this is something happening with Steve's blessing and not something dirty on the part of Disney, we can at least watch a new Kermit performance rooting for Artie to succeed; he would have more support. When we watch Kermit, we're given some freedom to sit back and enjoy the show instead of having our thoughts clouded by "what IS this?".
For many of us, Steve IS Kermit now. When Steve goes missing and no one knows why, the frog goes missing as well even if someone has his hand in the puppet and is saying his lines with his best Kermit voice. Just as we have a strong emotional connection to Kermit - practically consider him a member of our families - the same feelings extend towards Steve. We want to know that he's being treated with respect and that the change is not something basically being done behind his back. The person on the throne needs to be an heir and not an usurper.
It's not like we even need every little detail. If something is going on with Steve's family for example, all Disney has to say is Steve is taking some personal time off to deal with a family crisis as he all hope he'll be back as Kermit soon. No personal details revealed about him or his family, but at least a general reason and an affirmation of his rightful place as the official performer. The silence is really deafening. No one is talking on or off the record - anonymously - and that is not a good sign. If there's a perfectly logical and fine explanation (Steve is recovering from voice loss, Steve is ill, Steve is taking a vacation to celebrate his 50th birthday, Steve had schedule conflicts), then why is it so difficult or taboo to say so. Again, just the barest most general statement is fine - huge details not needed - it shows that Disney is sympathetic towards the fans and not hostile towards them.
Regardless of the reason, we'll still critique Artie with the same microscope Steve was subjected to - commenting on the good, the bad, or the ugly - and we'll also be a little curious why someone pretty low on the Muppeteer totem pole was given this task - but we can at least be free to support him. We can accept him - accepting and liking are two different things. But as long as no one knows why Steve isn't doing Kermit, that's all we think about when we see Kermit. Our minds by nature won't be as focused on the performance as they are thinking of stuff outside of it. It was like how the opening sketch with Rudy Giulani on Saturday Night Live gave the audience the affirmation it needed that it was okay to laugh and enjoy the show again after 9/11. (The audience may have then thought SNL was either a triumphant comeback or another year of "Saturday Night Dead" but at least we had that emotional freedom to watch the show and hopefully allow ourselves to be entertained...though it still didn't free the performers to give lackluster performances or be called on the carpet if they did).