The dozens of statements of eye witness evidence - the massive damage that was done, the weapons used - even the Gunboat Helga firing shells from the Liffey - these can only be used 'indiscriminately' in the hope they might hit their target.

Not true Jim. There is no evidence of indiscriminate fire that I can find. You clearly know of none either.

" Subsequently the Helga II gained an undeserved reputation for playing an essential part in the Rising. (Most of the damage to Dublin's city centre was caused by fire, particularly at premises like the Irish Times warehouse and Hoyte's Druggists and Oil Works, rather than by shelling.)"

"On 25 April 1916 the Helga sailed from Dún Laoghaire to shell Boland's mill, and on the following day fired over the loop line railway bridge at Liberty Hall. In total the Helga fired only 40 rounds during the Rising, "
http://www.historyireland.com/20th-century-contemporary-history/tss-helga-ii/

"The log of the 'Helga' is rather succinct: "26 April. Proceeded up River. Stopped near Custom House. Opened fire on 'Liberty Hall' in conjunction with Military. Fired 24 rounds (8.00 am)."

"At the same time, British Army gunners had moved an 18-pounder field gun from Trinity College. They set up by the south quays by Butt Bridge at Tara Street, and proceeded to shell Liberty Hall as well. They had only shrapnel shells. These did not contain high explosive and would have the effect of a glorified but high-velocity cannon-ball."
http://www.theirishstory.com/2016/03/24/the-helga-and-the-shelling-of-liberty-hall/#.VxdkofkrKt8

No suggestion of indiscriminate shelling here either.http://www.rte.ie/centuryireland/index.php/articles/the-easter-rising-and-destruction-of-dublin

"Homes and businesses across the city were damaged by shelling of key rebel garrisons and widespread looting."
http://www.thejournal.ie/british-pathe-footage-dublin-1916-easter-rising-2683266-Mar2016/

Nothing to suggest indiscriminate British fire.