You are mixing numbers that don't go together.

OED (171k) is comparable in content to RAE + RAE Americanisms (93k + 70k = 163k) because OED is pan dialect. RAE core dictionary by itself is not the same type of coverage as OED.

The 1M+ English number is essentially a garbage number from a media tracking company called Global Language Monitor and includes things no serious dictionary would include. 300k+ is for a very comprehensive legit Spanish dictionary with technical and historical words. Those two numbers aren't comparable.

"which you admit is a far lower figure in Spanish vs other languages." no you just misunderstood, the numbers are very comparable.

Looking to your perceptions of ngrams in pop lyrics is not a great way of doing linguistics, there are in fact many alternatives in Spanish for expressing emotions about love, whether you are aware of them or not, or whether song writers over use certain words. English lyrics repeat an awful lot of "love" "heart" and "baby".