You don't have to buy their pans. Most combis use standard hotel pans. Mine use 12 x 14 pans , IIRC, and are available at restaurant supply stores and Amazon in various depths and perforated and non perforated. https://www.katom.com/cat/hotel-pans-food-pans/guide-steam-table-pan-sizes.html?gclid=CjwKCAjwlujnBRBlEiwAuWx4LUDayflbTFJr8cBbUdYMtWb_FbJIxf_aN72_DvnPDzDikwLq-x82fxoCVwAQAvD_BwE has a chart explaining the sizes.

Also, while standard half size sheet pans don't easily fit into Miele's CSO, with a little bit of wiggling, you can get them in there. I'd rather use the properly sized pans. But in a pinch, I have used my normal half sheets and it worked fine.

I did have to remove the telescopic slides though. They were just a little bit too big.

When I bought my CSO, Miele had a promotion that gave me a ton of pans/sheets. Not sure, if that's still active. But I am doing pretty well now. The only thing that I added was another small perforated pan. I found that I regularly need more than one of those.

My understanding is that, with the current technology, a standard-sized oven would require an inordinate amount of steam/water in order to work. If I'm incorrect, maybe someone could chime in?

I bought quarter sheet and jelly roll pans for mine. If I need a half sheet - I use my 30” wall oven. It would be nice if they made a 30” XL size oven but if you look at Miele and other European oven suppliers - the standard size is more in the 24” range. I doubt they will invest the $$ for a wider CSO with a limited market, but I could be wrong.

The Miele XXL and Thermador 30" CSO's are wide enough - it's just the wire racks that hold the pans need to be re-designed. That's a very easy fix and both refuse to do that ('ve asked!). Yes, you can squeeze a pan in there, but it doesn't sit level - it's cockeyed to one side.

Yeah, we Americans are a little spoiled here. Apparently, internationally, there is no standard for pan sizes. At least for residential ovens, every manufacturer does their own thing. And they frequently change pan sizes from one model year to the next.

The US is unique in having standardized on the dimensions of half sheets and full sheets. The reason this works is that American ovens typically come with wire racks that you can set these sheets on.

Non-US ovens more frequently only have slides on the oven walls, but don't come with these wire racks. Instead, the manufacturer provides custom-made pans that go into these slides. That's also why these pans all have lips on the sides, whereas American pans tend to have vertical sides. Also, the non-US pans tend to have ventilation holes on the sides; something I have never seen in the US. And enameled oven ware is much more common than plain aluminum (with all the usual quality problems that enamel can have).

Here is an example of what a typical sheet pan would look like:

On the other hand, many vendors on non-US Amazon websites do ship internationally. So, if somebody was really curious, they could try. It might just take a few tries to find a competitor's cookie sheet that actually fits. Another possible option to look at is this sheet pan for Bosch ovens. Again, it's close, but not quite the same dimensions. It's cheaper too.

Finally, because there is no standardization, a lot of consumers buy adjustable sheet pans. I am not a huge fan. Too many things that can go wrong. But I understand why this product exists.

One thing to consider about the Miele Ovens is they do include a “full size” pan and perforated baking pan that can be used in the oven modes as well as two pans that can be used in the steam setting. I dont know if these will fit on your sink but should be close. I have purchased a 1/3 gn 6” deep pan from a local food service store I use for linguine/spaghetti . I find all but my 1/2 sheet and Williams Sonoma cookie sheet pans fit in the CSO. The jelly roll pans I have found work for almost all of my needs where I might use a 1/2 sheet pan. You can always put a smaller pan on top of your 1/2 sheet that fit in your sink for service.

I bet wolf brought the Swis CSO and rebadged it to get into the market quickly. Look how long it took them to get a DW to market.

The new Wolf 30" CSO can hold standard half-sheet pans (18x13)

https://www.subzero-wolf.com/wolf/ovens/steam-oven/30-inch-m-series-transitional-convection-steam-oven