English does have more loanwords than most languages have words.

Small languages that are dying out, maybe. Contemporary standard German is filled to the brim with loanwords from French, Latin, English and even Hebrew.

If I remember correctly, they both stem from some proto-Germanic language and they continued development independently of each other.

Old saxon, specifically. I don’t think there’s anything proto about it, it was just an old form of a dialect that was common in Germany until about 200 years ago.