​I (along with many others on this forum) have had the complete opposite experience as to what you have described. As someone who maintains both platinum on spg / bonvoy and globalist on Hyatt, I find that I am upgraded on Hyatt about 75% of the time and less than 25% of the time on Bonvoy. Over my last 5 stays on Bonvoy (since the IT merger), I have not been upgraded a single time. I have been upgraded on 5 of my last 6 stays at Hyatt properties.

Couple of other anecdotes: I stayed at the grand Hyatt baha Mar over new years when the hotel was completely sold out. I wasn't able to secure a suite upgrade in advance so I had resigned myself to a regular room. When I checked in, they had upgraded me to a residence suite that overlooked the fountains and that had a balcony that had a perfect view of the new years fireworks... I had a similar experience at the Hyatt in Huntington Beach (no suite upgrades available in advance but was given a very large suite upon check-in)

Long story short, I've been more than happy with world of Hyatt and they've certainly inspired increasing loyalty from me over the last couple of years. I've shifted most of my spend to WOH and I'm questioning if it's worth it for me to continue maintaining platinum elite status at bonvoy. The only issue is that I have 2m points to burn at bonvoy so will likely need to stay at the hotels...