You’re assuming they will never raise the rental pricing, which seems unlikely.
And yeah I paid for two upgrades before Adobe moved Lightroom to rental only. The pricing was quite steady. Keep in mind Lightroom had no DRM baked in. No licensing checks, perpetual three seat cross-platform license, etc., etc. That $10/mo is for one seat only.
If the cost to the consumer were close Adobe wouldn't have spent the engineering effort to integrate Lightroom with all of their licensing software and incur the cost of having to keep the rental servers running. You can't predict the future but based on the steady pricing (both rental and perpetual licensed) the rental software is unambiguously more expensive for the consumer.
Lightroom upgrades cost about $80. According to the wiki page Adobe rents Lightroom for $10/mo. That upgrade would only get me eight months of access.
Sure, they've provided a ton of shareholder value for those subscriptions. Customer value? Not so much.