1. web apps don't need an expensive development environment. So you don't need to buy or rent a mac just to submit the app to apple
2. Tools are free, no 99$ fee for ji'ust the right to submit apps.
3. No person can reject your app because you violated an vague rule or are thrown out because apple provides an very similar app.
On the web, no one can force you change the app you already shipped and no one can change the rules under which it operates. On iOS, Apple can and does do these things, which cost you money to keep up with.
This isn't entirely true, in practice.
It's not as bad as iOS, but browsers & search engines can effectively change the rules on you, even on the web. APIs you rely on can be deprecated, browsers can change their behavior, search engines can change your app's visibility, etc.
1. A lot of people are doing their web development on a Mac, so this becomes a moot point.
2. While it does cost $99 to get in the store, the app can be used by millions for no additional cost. Hosting fees for a web app will grow along with the user base. Even without users, a domain plus a basic hosting plan will easily be more than $99/year.
3. This is valid, but a problem for some apps more than others, and it doesn’t relate to cost.
$99/year is just to host the 'client-side'. Most likely you still the backend so that cost is still the same.
I saw no valid counterpoint for the question "Does it cost more to build an iOS app than a web app?".
1 is obvious, you can develop for web everywhere but can't build iOS apps everywhere. 2 also apply for web but without the $99 fee. 3 is the most nonsense defense of apple gatekeeping I read today, it obviously relates to cost if apps get denied for marginally competing with Apple.