I understand 'worst sales' but 'worst performance' doesn't really fit. It's in my opinion this is a fantastic performance on the market. With right to repair, longer software support, some models with replaceable batteries, we can use the phones longer and make the industry more sustainable and consumer friendly. For the last years already, the model feature upgrades were marginal and it's fine that way.
In the future, I'd hope for further technical and regulatory development in that direction, resulting in further reduced annual sales numbers.
In the 1st step, maybe a year ago or so, they updated the Kasa app (v 3?) to only function with account and while being logged in at TP-Link servers to use your devices. And in now the 2nd step, they integrate Kasa into Tapo, which was always account-bound. The 3rd step is then probably the discontinuation of the Kasa app.
Kasa was their more premium product line, that was usable without internet connection and without manufacturer account - which is why I paid more to get those instead of the cheap Tapo products. But now my 'smart' power outlets are in a box in the basement collecting dust and I cannot recommend anyone to spend money on TP-Link smart products, as they remove features after sale.