Not knocking on your strong opinions on Russell Allen, but I can't imagine who would have to sing in Dream Theater for my fandom to come for a screaming halt. If it were someone I vaguely dislike but who is a technically sound singer and can actually cover the range of Dream Theater songs, I'd still give them a shot. When I was asked by the universe if my fandom is brought to a screaming halt by James singing the way he does lately, I said "no" and bought tickets for shows in 2022 and 2024 knowing fully how he was going to sound, so
I went to DreamSonic not because of DT, but because that was a great lineup.
Getting to hear Devin sing TSCO was an epic moment, as well as Tosin playing along as well.
Regardless of JLBs vocals I still had a great time. I jammed out and sang along. It was more than just seeing my favorite bands, it was the experience of the show, and Dream Theater shows are about the songs for me, which I don't care if JLB sounded bad, I love the songs enough to sing along to them.
I even did the same when I saw them opening for Maiden. Although the set was like a singles set, I still had a blast.