I don't really have the answer to your question, but since no one else has chimed in, I'll give you my 2 cents worth. We probably need to update that expression.
My guess is that the two are about equal on reliability but have no real data to back that up. Neither is sold in the big box stores, so cost wasn't the primary factor in design. I would recommend you compare features on the two to be sure neither is missing something you really want, and if possible, take them out for a test mow. I bought a Regent about 12 years ago after 15 years with a Broadmoor that was already 10 - 15 years old when I bought it. The Regent served me well for the 2-3 years I had it (before moving to a push mower house), but I was surprised at how flexible the frame was both while mowing and blowing snow. If you went over a bump with one wheel, you could feel the frame twisting! If all else was equal, I would still buy the Regent over the Deere, just because I like the way it pulls the mower instead of carrying it.
I was in Quality and Reliability engineering and management for 30 years, in a couple of different industries, then spent the last two years before retirement (about the beginning of Covid) as the service writer for the lawn and garden section of our local John Deere dealer. My biggest learning while at the JD dealer is not to buy any of their products that start with a 1 or have an E in the model designation. They were clearly made of cheaper components (deck spindle bearings and transaxles come to mind) and lighter weight fabrications. The sales department's line was "It's the best $2000 tractor on the market, but it's still a $2000 tractor." They tried to sell customers up to the bigger tractors but wouldn't turn down a sale (by the way, you could get the same tractor from us or the big box store for the same price, but we delivered it free, and would pick it up once for warranty.)
Similarly, a lot of Simplicity dealers will try to sell you up to the Broadmoor to get the heavier components. Heavier frame and transaxle come to mind.
JD was very good on warranty, they call it bumper to bumper, excluding only wear items like belts. If the belt died as a result of some other component failing, the belt was covered too. Didn't matter at that time if the unit was purchased new or used, we could check the serial number and tell if it was covered. Simplicity doesn't cover anything except to the original purchaser.
I felt that the 300 series and up from JD were very good, well designed and well-built machines. I rarely saw a 200 series. I don't really know why we didn't sell many of them. When we did service one of them, or the older LT100 series for that matter, they seemed to be decent tractors. But I cringed whenever someone brought in a 100 series, telling me he (or she) expected typical John Deere quality, since it came from the same factory. Of course, I couldn't tell them that the factory it came from had less to do with reliability than the initial design. No matter how carefully and skillfully a product is manufactured and assembled with inferior and/or lighter weight components, it's not going to be the same. The other end of the shop saw similar issues with bigger tractors with an E in the model designation.
Personally, I'd recommend either a 300 series JD or a Broadmoor or up from Simplicity. But if you got 19 years from your LT, you probably took good care of it, and don't have too challenging of a yard.
I can't tell from your question if reliability is the primary or only deciding factor. If it is, I'd certainly go up to the larger size tractor, but get fewer fancy features (power steering, lift, suspension, etc.). These components by themselves are pretty reliable, but the more components you add to the product, they math says reliability will suffer by some amount.
