The press release says it will "power a selection of flagship devices from key customers including Motorola, iQOO, OnePlus, OPPO, and Xiaomi.†The real flagship SoC is the Snapdragon 888, so Qualcomm's use of "flagship" here definitely belongs in scare quotes.
The Snapdragon 870 isn't just similar in spec to the 865—Qualcomm describes it as "building upon the success of Snapdragon 865 and 865 Plus" indicating it's another plain clock bump with no design changes.If these are the exact same chip, this is an odd decision since the Snapdragon 865 SoC design was a stopgap design.
If we assume the previous-generation chips are dead, the 870 is now the only chip in Qualcomm's modern lineup to feature a 4G and 5G modem on a separate chip.
In the land of marketing logic, I guess Qualcomm's new model number will stop casual observers from calling this "last year's chip." Unfortunately for Qualcomm, marketing has no power here.