“Gem Value” calculations aside, this seems to be true. For the record, t2 and 3 of raid on everyone don’t allow you to complete the event unless one person is getting higher tiers. Since progressing further in raids increases how efficiently you are able to use your sigils if you play perfectly (higher boss level = more boss damage per sigil spent), people spending a little bit more in raids can cover multiple people spending a little bit less. Since one sigil in Invasions is worth at most four towers regardless of how far you have progressed, a couple high spenders can’t offset several low spenders and the event is more costly overall.