The two events are ones you cannot compare.
You have to go to the brunch. Simply amazing. Go hungry. Simply the very best. Must have reservation the first day, very few cancel.
High Tea is o.k. Taking tea at other hotels I've been to has been much nicer. I'm glad I did it, I'm not sure I would take the time to do it again.
If you do not get reservations for the tea and then decide to go chances are you could easily get in. There were only two other tables full when we were there. The biggest jackpot Bingo game was going on at the same time so that may explain the lack of participants.
Have fun and eat well. Do not skip the homemade pesto at Brunch.