Yeah there isn't enough data to really pass judgement either side.Well, clearly I don't want him to burn out. The question is if he will. Now, I'm certainly no expert in the area as most of us aren't, but is there any evidence that you risk burning out faster if you do all three Grand Tours? Doing the three Grand Tours, the five monuments and Worlds is 69 race days. Perhaps on the higher end of the spectrum, but definitely not unheard of. There's of course some cumulative fatigue in the Grand Tours but on the other hand, a one day race is much harder than many Grand Tour stages. Besides, Pogacar is a physical freak and should be able to do a harder schedule than most others.
I often hear former riders say it's also mental thing than physiological. Living in the GT bubble and competing etc. having these intensive periods of stress without time for your mind to go on vacation.
Thing is Team Pogi doesn't have the data yet on whether or not his body is too overworked to do Vuelta or if he needs a break from the 3-week bubbles. He hasn't done Giro-Tour before so it's a bit uncharted territory for them. Both in terms of how his muscles are reacting and in terms of his mental state.
IMO it would always be a last minute decision if Pogi decided to go, but I am sure the plan was always to "only" go for Giro+Tour double which is very impressive in itself.