Samsung makes a lot of cheap and mid-tier devices with little RAM and not so powerful SoCs. Google also uses slow SoCs, but at least they compensate in hardware.

If you just buy a high-end phone, Samsung is generally fine. If you buy anything cheaper than that, or god forbid buy a phone through a carrier that pumps it full of crap, you're gonna have a terrible time when apps get slower and bulkier and shittier and the hardware shows its age.