I believe this isn’t true. Convocation of Decay’s finale has only been tweaked to be more difficult in the June 23, 2020 Grail Knight patch (Patch 3.0) - the same patch that tweaked many map end events / finales. This thread was made on July 8, 2020, only around 2 weeks after the Grail Knight patch, so the complaints were rightly timed. I remember pre-Patch 3.0, and pre-exploit Convocation - and it is not as difficult as its current state.
The difficulty tweak is not listed in the patch notes (unsurprisingly).