Could be wrong as I'm a pretty low level marth here, but I think that's a really iffy generalization and way too vague. I would say it depends on percentage and whether its Falcon or spacies (weight matters hella). For example, anything below 35% on a spacie doesn't really combo unless they DI wrongly, and even at the dreaded 40-60%, a DI-down-and-in can make uptilt not chain into itself, sending the spacie backwards at an awkward angle (Which can be regrabbed if they were upthrown first, but you're talking about raw uptilt).
On falcon I can see it making some longer chains just since he's heavier and has a bigger hit box but I still find it hard to imagine 5 if the DI is right.
20XX CPUs often prioritise random DI unless he's set it to DI one way only, and I don't think there's a setting for optimal DI (that'd be a little too complex I think.) It's entirely possible the 20XX cpu isn't DI ing well. True combos mean that they hit no matter what DI if you perform them right (Like fox upthrow-upair or marth upthrow-uptilt at certain percents), and I'm fairly sure multiple uptilts aren't one, unless you add grabs in between, and even then not 5.
