It really depends on how you look at it, you may call it a 50% discount or you may call it a 100% tax, being on the "normal transaction" side, it would seem as though you are getting a 50% discount compared to the rest, being on the other side, it would seem that you are paying a 100% tax compared to the rest, if we think of block space as goods sold at the market, at the end of the day, a "normal" person can buy twice as much of those goods with the same money compared to those "weird" people.
Yes, but compared to the current policy, it's not correct to call it a "tax" or "discrimination", because nothing would have been changed and these transactions are even favoured because blocks would be, on the whole, emptier. And if the blocks are not full, like it was the case many times even in 2022/early 2023 before Ordinals came up, then there is no tax at all.
With the other part of your post, you are correct - it's possible that fee income goes down if demand is not enough. To avoid this, in the block size debate models for a flexible block size were proposed, where the maximum weight is adjusted by demand or there are incentives to miners to adjust the blocksize carefully if needed.
Monero (which was already mentioned in this thread) is an example how such a policy could look like. In contrast to Monero, however, Bitcoin needs slightly stricter parameters, because of Monero's tail supply which ensures they get rewards infinitely, so the necessity of a fee market isn't that pronounced on XMR.
So you could combine the "payment transaction discount" with a "flexible blocksize" policy. In this case, if the minimum max size is set too low, then the contract/Ordinals transactions could pay a "tax" indeed even compared to today. I think it would make sense, if such a change was decided, to ensure the minimum max block size is never lower than the current 4 vMB.
Anyway, such a policy is, again, meant as a possibility
if there is general consensus in the commuity of the need for a block size increase, and that would be decided only if demand justifies it. Simply: instead of moving max block size "straight" to 8 MB, one could change the weight formula in a way simple payment transactions pay half the fees.
Even if the current fee situation is a bit annoying, in my opinion we have not reached the point, and my hope is we'll never need it due to sidechains/LN improvements.