What makes heroin superior is the potency (twice as strong mg for mg) and the fact that there are less side effects with I.V. administration.
That being said if you have access to pure morphine vials and don't mind the pins and needles. Then you should probably just stick with that.
I would like to see something that supporting your statement that "
...there are less side effects with I.V. administration". Less side effects compared to what? The side effects of morphine?
The effects of opioids are dependent on the drug crossing the blood–brain barrier and accessing the central nervous system. This suggests the blood brain barrier plays a central role in both the benefits and risks of opioid use (1). Opioid transport across the BBB into the CNS is essential for the euphoric effects of opioids (2). It also seems that the efficiency with which an opioids crosses the BBB influences the level of euphoria. Oxycodone is transported into the mouse brain in concentrations six times higher than morphine (3). From the efficiency with which Oxycodone cross the BBB and the following increased euphoria you might be able to conclude that this is one of the things that make oxycodone so dangerous. The level of euphoria a drug can produce is obviously related to the abuse potential of said drug.
Back to heroin. Heroin has a potency twofold greater than morphine and crosses the BBB more readily than morphine (4) as you write yourself. Although heroin is similar in structure to morphine, this drug is acetylated and therefore more lipophilic than morphine which increase BBB permeation (4) leading to an increased potency and euphoria . The increased efficiency with which heroine cross the BBB relative to morphine
So yes, heroin is more potent than morphine. But I haven't seen anything that indicates that heroin has less side effetcts.
1) Schaefer, C. P. (2017) The opioid epidemic: a central role for the blood brain barrier in opioid analgesia and abuse. Fluids Barriers CNS. 2017; 14: 32.
2) Yaksh T.L. and Wallace M.S, (2011) Chapter 18 : opioids, analgesia, and pain management. In: Goodman and Gilman’s: the pharmacological basis of therapeutics, 12th ed. New York: McGraw-Hill; 2011.
3) Bostrom E. et al., (2008), Blood–brain barrier transport helps to explain discrepancies in in vivo potency between oxycodone and morphine. Anesthesiology. 2008;108:495–505. doi: 10.1097/ALN.0b013e318164cf9e.
4) Kaiko R.F. et al., (2008) Relative analgesic potency of intramuscular heroin and morphine in cancer patients with postoperative pain and chronic pain due to cancer. NIDA Res Minigr Ser. 1981;34:213–219.