I Was thinking on Crazy Taxi.
The problem with ports is that they're all over the place.
CT collection on PSP was 30fps (with some extra content) - but outside of that it was an exact port.
On the flipside - PSP Outrun C2C actually DID run 60fps (90% of the time), and that was graphically a significantly more complex title than CT, and a port from XBox to boot.
And then we also had a plethora of XB360 ports that on PSP all mostly retained the full experience of HD counterparts (Lego games, DOAX etc), despite scaling from 512MB down to 20.
TLDR - just looking at 1-2 ports can be completely misleading about what the system actually did 'in practice' - let alone on paper - which is a whole other story - these handheld porting efforts were very short staffed and under funded as a rule since the sales potential didn't justify anything more.
Blue stinger vs Silent hill shattered memories
SH games on PSP were also a bit of a small miracle. Tech-wise SH:0 actually exceeded PS2 Konami's efforts in some ways (it did get a competent PS2 conversion afterwards though), amusingly being a 60fps game at points (on Vita, fully so with the faster CPU in BC).
Then why do ports from the dreamcast have such cut back lighting framerate, geometry and textures? All while running at on 40% of the resolution?
Resolution and content scaling was mostly a function of the display/dimensions. We were still in the era where consoles had no competent AA solutions available, so taking 10-20k poly models to that tiny screen just looked awful. And also memory limitations (for a long time - PSP only gave 20MB usable memory to games, which added reasons to cut down asset resolution).
Performance is a different story - ports are driven by limited budget first, everything else second. So if 30fps is all you can do in 3 months you get to ship the average one, 30 fps is all you do. But part of the problem was that despite 'on-paper' looking like any other console of similar specs, the memory
performance was a massive drawback. So you could treat it like a mini PS2/DC but it would not perform like one without special care - meaning most ports also didn't.
To give another analogy - PSVita eventually received PS2 collection ports of Jak, God Of War Sly Cooper etc. Except for Sly -
every single one of them ran between
2-3x slower than PS2 original version (3x is not a typo - Jak 1 actually runs between 15-20fps on Vita, and that remains true even if you overclock the system).
Now clearly - this wasn't a case of 'PSVita was so much weaker than the PS2' - but it had a lot in common with what I said about ports above.