The $400 Dell was a Ryzen 7 and 1 TB SSD. Why is this one better?
The dell had a Ryzen 7, true, but an old one, 5700u. The i5-1335u is 2 years newer, and is at least equivalent, or maybe much better, depending which benchmark and which tasks.
Screen: b&h 300 nit vs Dell 250 nit.
Battery: 56.6 whr vs 41whr
keyboard: b&h backlit vs dell non.
fingerprint Reader: b&h yes, dell no.
Webcam: 1080p vs 720
Extra usb c port on the b&h, and better wifi chip.
What the dell has going for it is 1tb ssd vs 512, and it's .45lbs lighter because it's smaller. (15.6 vs 16 inch is preference, not a pro or con)
The main thing though is that the Lenovo slim 5 is metal and built better than the plastic dell Inspiron 3525.
The thing is, most people could get the dell for cheaper than list, with amex offers, credits, and cashback portals. So it's really a question of a $320 dell vs $400 lenovo.