Honestly, I would rather see (you) bunq developers focusing their (your) time and effort on the mobile apps than following the trodden path of what other banks do.
I just migrated to using bunq as my primary SEPA account (even though I'm not based in NL and have SEPA payment accounts in half a dozen other countries). Why? Because most other bank's apps (or mobile sites) have limits on what I can get done: restricted international payments, no direct debit management, missing support facility, unwieldy authentication schemes, etc... and maybe above all: clunky interfaces that just don't work efficiently. That is not to say that your app's perfect (far from it!) but...
I do believe that "being mobile first", and doing it rightly and nicely, is bunq's differentiating factor. That's where you have the edge over other banks.
Four additional thoughts on this:
1. I can imagine developing a full-fledged banking website from scratch would be a huge task, taking massive amounts of time and effort. And it requires additional authentication methods and their inherent complexity...
2. ...and security measures and precautions. My iPhone is, by design, my most technically secure computing device. By far more than desktop browsers.
3. I honestly don't see that big a problem with having no access to a smartphone. In "my" reality, few people (at least under the age of, say, 45) would "just do without one" for more than a couple of days. They would, at least for essential apps (Whatsapp) use their old phone, get a loaner phone from their service provider, borrow one from someone in the family, etc... Even an old iPhone 4S should run the bunq app.
4. It's not like you are going to get away with a pared-down/stopgap website as a "backup" or "emergency" solution. Once you commit to and release, people will incessantly bug you about feature parity with the mobile app.
Sure, having a somewhat functional desktop website would be better than not having one. But the bottom line is, development (and support!) effort would be quite substantial.
I'd rather see you pushing the envelope of what mobile banking can be like.