First off, this is no more an upgrade than moving from Apple to Android or vice-versa, is an upgrade. It is a conversion to a fundamentally different TV platform - hence the loss of recordings & series-links, due to the HDD reformat.
There are many pros & cons on both sides, and innumerate past threads, but as a handful of of bullet-point headlines that you've alluded to and are current...
> Disney+, AppleTV, Paramount+ are only on TV360. V6 will never see these.
> Sky Sports HD multiscreen is currently only on TV360, but is being developed for V6 - just with no timescale.
> TiVo/V6 is unmatched as a recording box, whereas TV360 is a streaming device first with recording bolted on.
> TV360 will only allow you to set series-links for programmes that are listed in the current EPG. V6 can pick one up from a single OnDemand asset or "Search & Explore" entry.