I swapped to Revanced on mobile and a combo of UBO + sponsorblock on desktop after the most recent price increase. Definitely not regretting it after hearing this.
Like a sibling comment mentioned, I was considering that newspapers got non-trivial amounts of funding from ads. Classifieds in particular, if I remember correctly. If that's still not satisfactory, then just consider the case of free papers & magazines.
How? Buying the newspaper pays the people printing the newspaper and making the paper. Whereas not a cent from paying for internet service goes to third party websites like YouTube.
It's like saying stealing from stores is okay because paying taxes for the upkeep of roads is equivalent to paying for the stores.
Physical newspapers lost money on printing and distribution. Subscription fees and purchase price did not cover the cost of printing and distributing that bundle of paper. The vast majority of their income was from ads. So your argument is really even worse with that in mind - physical newspapers were more dependent on ads than internet websites. And even with that in mind, I don't think anyone would say having a robot cutting out newspaper ads to be stealing.
It's not really a poor argument. This was the understanding of how the internet worked before we decided to use the internet to replace TV. There was never a guarantee of payment to anyone running a public web server.
But I think you've highlighted exactly why net neutrality is terrible in practice (people effectively stealing bandwidth by blocking ads).
This is a terms of service violation at best. There's no theft, nor even copyright infringement.
The obvious parallel is Sony Corp. of America v. Universal City Studios which established that time shifting - recording a TV broadcast to play back later - is fair use.
Someone using a DVR with a "+30 seconds" button to skip an ad was not stealing from the broadcast company.