I don't know why the development story matters. If Dragon Quest maintained popularity, XI should have performed better than it did. I predicted around 6 million across the three version, because each one offered things the other lacked, encouraging double/triple-dipping. DQXI PS4/Switch and 3DS are essentially each other's remakes. Being accessible to a larger playerbase is the other factor to consider.
Don't worry you don't have to explain that lol. You'd be hard pressed to find anyone here who spoke against gauging success or popularity based on attach rates alone more than myself. But in the case of Rise vs World, the inevitable 300%-350% install base advantage of Switch over PS4 should be expected to translate to more than the increase we're seeing. I was expecting it to sell 4.5-5 million, which is a conservative figure compared to what many others thought here.
Going by attach rates, nothing beats World which launched to a ridiculous 33%~ attach rate at 6 million PS4's, and pretty much maintained it. I hoped that this was an indicator that the series may be growing in Japan (Peak popularity Monster Hunter sold an unimpressive 1 million on Wii), but Rise is under-performing all things considered. Rise launched to an (expected and fairly impressive) 10%~ attach rate, but it's not legging out particularly well with the install base in mind (slightly/moderately worse than I expected, but not exactly a shock).
The relationship between install base and software sales is certainly not proportional, but it's linear. The popularity of Switch just isn't being reflected on Monster Hunter Rise so far, and this indicates a slight decline in the IP's popularity in Japan.
It's actually kind of funny that Capcom refuses to release a Monster Hunter game on both Playstation and Switch. Would likely break Portable 3rd's record, but probably not when counting PS3's version.
@bold, A simultaneous release is just that difficult. Porting from PS4 or PS5 to Switch or vice versa requires basically making a new game. Capcom thought it was more worth it to do just that, and made Rise.