I don't know why most registrars have terrible interfaces.
I'm a Namecheap user and they just launched a new interface. I have not really *used* it. Just poked around, but honestly compared to anything I've suffered through before (Moniker - yikes!; GoDaddy - yikes!; Network Solutions - good riddance) it is a thing of beauty.
The key thing that I see is that when you look at a domain, you have a management nav ribbon.... actually I'm going to grab a screenshot.
But notice that Sharing and Transfer is right there every time you look at a domain. Click on that and you get everything you need to leave Namecheap. In my experience most registrars hide this and make it very hard to find. The fact this is so prominent shows, I think, their commitment to give you reasons not to change. One of those is they don't clutter things up with screen after screen of offers.
I thought they were pretty good when I started with them, but unlike the precipitous decline in quality I saw at Moniker, I feel Namecheap continues to improve... though I've only been with them a couple of years.
I haven't tried their bulk interface, but it looks like it would work great - screenshot attached with the dropdown expanded so you can see what bulk oeprations are available.
My needs are modest and I only manage a diminishing handful of domains (down to 25... soon to be 20).
I know Drastic has an account b/c I transferred a domain to him at Namecheap. I don't think it's a primary registrar for him though. But you can page him for his thoughts.