I forgot another source of ROI. As each landscaper reduces their prices their addressable market (people able to afford landscaping) expands. By saving time using AI, they are able to serve more of that market. So the actual ROI will still be positive.

And keep in mind this is one market with relatively undifferentiated players (landscaping services) that we are talking about. Markets where operators have more pricing power will be even better off.

If we follow your argument to its logical conclusion, any technical or capital investment by a landscaper is pointless. They may as well use manual lawnmowers, rakes instead of leafblowers, and go from job to job on bicycles instead of pickup trucks.