Is the dev time really that unusual, taking longer than expected?
As we hear over and over, and is undeniably true, AAA titles, particularly those compounded by Sony's production standards, are taking longer to make and more costly. Ghost of Tsushima will be 4 years old in June, and that's alongside Sucker Punch having worked on a PS5 port and the sizable Iki Island expansion pack.
For comparison, Santa Monica took 4.5 years to deliver Ragnarok after '18, inclusive of their own PC port support. Meanwhile Guerrilla took 5 years to drop Horizon 2 after its predecessor, with no title in between.
And while it's not lost on me that in both cases there were likely studio projects that were either canned (see: Santa Monica) or in development for another platform (see: Horizon VR), eating up dev resources, I do think the comparisons are reasonable and entirely in line with what we've come to see from a standardised and ever growing AAA production cycle. Compounded with the safe assumption that Ghost of Tsushima 2 is likely 'bigger' in content and more complex in production standards over its predecessor.
Ghost of Tsushima was really the last big new-franchise PlayStation 4 game, after God of War and Horizon, of which we got our sequels for. Sony's studios have all been taking ~4+ years to get their next big game out, with the only exception being Insomniac and the crack they must be smoking to pump games out as quick as they do. For Sucker Punch, a 4 - 5 year dev cycle for Ghost of Tsushima 2, for PlayStation 5, seems absolutely on par and a predictable standard not in any way indicative of "taking longer" or that some other software took priority.