The delay being less than 2 hours is neither here nor there if your rebooked flight entailed leaving more than an hour earlier. The datum time is measured from your originally booked airport, i.e. LIN. Since it takes ~1h20m to get from LIN to MXP by public transport, BA would have needed to rebook you on a flight scheduled to depart MXP within a very slim margin (roughly 20 mins to 2 hours after your scheduled LIN departure time) to avoid paying compensation.

I have been in a very similar situation in the past (STN vs LCY) and looked into the case law at the time - my view is that unless the above parameters are met, you're entitled to compensation through a combination of Azurair (which dictates that moving a flight forward by >1 hour constitutes a cancellation with no ability to reduce compensation for early or <2 hours late arrival) and WZ v Austrian (which dictates that for a diversion to a nearby airport serving the same city or region, the arrival time at the booked airport is what counts).

Obviously some degree of 'reading between the lines' is required since neither case explicitly covers this scenario and indeed WZ was only about a diverted arrival rather than departure., But I would struggle to see how, based on the principles underpinning those rulings, having to leave >1 hour earlier to get to another airport would not give rise to compensation.

Appreciate you may not want to pursue this one to Court in view of the above, but a CEDR submission is not particularly time consuming and IMHO worth a shout.