I would argue that's part of the appeal the way it uses fan service so it doesn't get old. It is so over the top and exploitative that it becomes very enjoyable because of that laughable extremes.
That's...literally the opposite of what I'm saying DxD is, though. I'm arguing that it's very milquetoast, mild and cautious relative to a lot of its contemporaries. A series that uses fanservice in increasingly over the top ways and plays around with the tropes of the genre in that fashion is To LOVE-Ru, or High School of the Dead, or Shimoneta. A lot of popular ecchi series use that formula. DxD is the fundamental opposite of that, though. It has an overreliance on one type of shot - basic exposure - and it doesn't push the boundaries or do anything interesting with that at all. It doesn't move forward with basic exposure shots. It doesn't push the envelope in any way. It's very, very circular with it. You see boobs. You see panties. You see boobs. You see panties. It's the type of fanservice that's only exciting or interesting if you're not used to anime fanservice. It's the very stereotype that a lot of outsiders *have* about what ecchi is and why they say they hate it so much.
I mean really, most of the time it doesn't even deviate from using the same setup to each fanservice scene, i.e. clothes dissolution is probably 3 or 4 out of every 5 fanservice scenes in DxD. And unlike TLR with anime falls and how it handles that trope - progressively taking that basic trope and maintaining a consistent escalation of it throughout the series, where early on the anime falls are anime falls, and as it goes on we're hitting points where Rito is hitting his foot on a remote and somehow doing an anime fall on his entire harem as a result of that - DxD never escalates the trope it uses most. The first clothes dissolution shot is the same as the second, which is the same as the third, and the same as the 200th. That's not making it more and more absurd. This isn't being over the top. This isn't being extreme with its fanservice. It's basic exposure on loop, never actually doing anything particularly interesting with the same fucking type of shot.
I think DxD is pretty limp-dicked about how it incorporates ecchi, if anything, but take that with a grain of salt. If you like basic exposure or if you like it kind of tame or soft like DxD handles it, that's all fine. But I don't think DxD even bothers trying to do anything interesting with its fanservice. It's 100% content resting on its laurels and being extremely repetitive and tame with it. Do I think less of it for that? Goddamn straight I do. Does that mean that the preference for how DxD does it is invalid? Nope.
Also, Sora no Otoshimono. Trinity Seven. Dakara Boku wa, H ga Dekinai. Zero no Tsukaima. Majikoi. Is a harem MC with the type of personality Issei has *really* that special? It's an archetype that exists in fucking spades and yet people want to act like it hardly exists. Would also hard disagree that DxD's cast is better - or even just equal to - any of the series I'd mentioned prior.