If the upper prices keep rising, the discounts will rise as well, and I don't mean "£90 ticket, 80% discount!" either. At the moment, you can get half price tickets from, say, TKTS for around (and under!) £30. If the upper prices keep shooting up, you eventually won't be able to get half price tickets for less than £45 anyway. That's just one example. And while top price tickets are shooting up, that doesn't mean that the lesser-priced partial view tickets will stay low; if the basic ticket cost is increasing, there's no reason why that wouldn't cover *all* the basic ticket costs. The balconies, partial views, and discounts are going to increase as well. Plus, y'know, this doesn't match with normal inflation, because wages aren't rising to match or anything right now, so it's not even justifiable.
The rich people paying full whack for the top tickets will only subsidise the discounts for so long; eventually the entire system will come crashing down around our ears like a house of cards where someone's tugged one out of the bottom row. MUCH better to be sensible about it now and gently deconstruct the house of cards one card at a time in a sensible order. DO YOU HEAR ME, PRODUCERS? FOLLOW THAT GRANDAGE!

Plus shows that cost too much won't run so well.
Sunset Boulevard had a sold-out run in Newbury. Now they're charging expensive West End prices and not doing so well. It was critically loved, but it's not shifting tickets, not at that price. Whereas the Donmar West End season, probably my most favourite non-RSC related theatrical thing EVER, is producing critical successes that are selling out at ever-so delicious prices. I'm willing to bet real money that Donmar are making far more money out of their sold-out cheaper houses than RUG are making out of their sadly-empty full-priced
Sunset. And shows that aren't selling enough never last long. If people can't afford to see shows, the shows won't stay open. We don't just need people to see shows to subsidise our discounts, we need people to see shows so that shows run!
There are many things involved here, and I think sensible ticket prices can only benefit everyone in the long run. Yep, even the performers. Don't worry about what cheaper ticket costs might do to their wage; worry about what an early closure will do.