I am not an OP-1 user nor am I a TE fanboy but I owned a Model:Samples and the simple fact that you cannot even sample on it and it doesn't have any synth capabilities cannot make it a candidate. The digitakt is not a synth either. Same with original Novation circuit and with Novation you'd have to buy both the circuit track and the circuit rhythm if my memory is correct to be able to both record/sample and use a synth. MC-101 seems completely different in term of ergonomics.
I wouldn't say any of them would be an alternative.
I think OP-1 is overpriced because there is nothing like it. I mean a secondhand laptop with a 69$ daw such as Reaper can do more, an MPC is more complete. But people who see the appeal of the OP-1 probably already have a computer and a DAW so this is not what they are looking for. They want a toy to make music.
I am not in the market for such a thing but I guess it is not that overpriced if some people are willing to buy it at this price.