As promised, I'm here with my update/outcome regarding the claim for a cancelled BRU-TRN flight by SN for technical reasons, where I re-booked via MUC on LH and arrived 5 hours later than scheduled.
The claim seems to have been accepted for a compensation of 250 eur.
From the e-mail received:
it appears that your flight SN3195, Brussels - Turin, of 04th February 2019 was cancelled because of operational problems.
In line with Regulation (EC) No 261/2004, I confirm that we will offer compensation to the amount of EUR250.00.
By the way, regarding the point that having chosen the "longer" option made me ineligible for any sort of compensation: if EC261 applies equally to any EU airline, then it seems that for flights under 1500 km, arriving late than 2 hrs entitles to 125 eur compensation. So, even if I had chosen the LIN+Bus option, I would have been eligible for a compensation of at least 125 eur.