I just have so much trouble buying the whole "we didn't anticipate people using his +1 on enemy creatures!" because Arena literally warns you when you target your own stuff with it, so at least the people who programmed the set were thinking of it as primarily good for that.
Firstly, that warning is automatically generated because it makes the target lose all abilities. Remember that code for MtG: Arena is generated via parsing the card text. Virtually nothing is hand-coded for exclusively for a single card.
Secondly, Arena usually starts implementing a set weeks after the set is "locked in" because the printing pipeline is longer than digital's. We give feedback about what's likely to be easy or hard to do during the design process, but it's set pretty much in stone before we start committing code. I look forward to the day when Play Design can iterate on a set in Arena, but that's still petty far out. #wotc_staff