Are you saying modern car infotainment systems have fewer resources allocated to the UI?
This was in a time when far fewer instructions were accelerated on the cpu, and my cpu at the time was something like a 66MHz 486-dx2, and even the (Frauenhofer) mp3 codec wasn’t as optimized as it was later.
Relatively speaking: Yes.
Response lag is always because the hardware is chugging to process all the bits in time (they're not in time). Between underprovisioned hardware and shittily written software, hell yeah fewer resources are allocated to the UI.
We need a small supercomputer's worth of resources allocated to bring the software of today up to snap like it was the 90s.
We're using small MCU (not CPU) to drive 480x272 or 800x600 screen. 240Mhz, 8MB of RAM. For example on ESP32-S2 or ESP32-S3.
If you had GPS, bluetooth, wifi, etc. to the mix, yeah that's a challenge and you need to make your UI pretty simple.
Despite that, automotive graphics ramain laggy because they normally build something barely gpu accelerated using java or QT or something else laggy by nature...
Anyway, when you're designing your UI, you've to take into account the computation power available and design around that, otherwise you're doomed.
Basically anything that involves copying pixels or solid fills without per-pixel calculations. 60fps at 800x600 is 28.8Mpixel/s. Copying and filling at that rate should be achievable by a 240MHz CPU with some tight coding. The rest is 2d geometry, mostly axis-aligned, with relatively few edges. That's not demanding at all.
(I used to write 2d and 3d rendering engines for slower CPUs than that.)
A GPU is necessary for fancier effects like fades and shading, but the basics can be smooth on a CPU and the fancy stuff too if confined to smaller areas.
Also, for the car, people would be happy enough if it could do a consistent 30fps I think.
Those annoyingly slow GUI updates you tend to see on TV set top boxes are not slow because of the hardware... it's usually the software not being written with sleedy rendering in mind.
All that said, you're right that if there's a GPU or even just a Blitter, it should be used and then the CPU speed almost doesn't matter as the geometry calculations are so simple.