It is NOT historically uncommon for the presidential candidate to chose the person who got 20% of the primary vote as a running mate. I also think that the RNC has done some polling if this axios article is legit. Regardless, we need to support Trump.
Maybe over a long period you are correct, but in RECENT history it has been a standard practice for Republican presidential nominees to have running mates who were NOT primary opponents. I believe the Reagan-Bush ticket in 1980 was the last one where two primary opponents ended up running together for the GOP.