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".

- Galician (easy mode, a Romance)

- Basque (they lived nearby the Castillans influenced Latin enough for Spanish, so that's a given)

- Catalan (another Romance)

- maybe Iberian, I'm not sure, through Basque

- Celtic, a common word like perro (dog) it's Celtic

- Gothic -yes, Goths, such as sala (living room), casa, (house) guardia...

- Arabic (most words with al- )

- French (carnét/garage...)

- Italian (most of the artsy stuff from the Enlightenment, such as piano)

and whatnot.

If you just pick up with the huge lyrics set from Spain you will find tons of different poetic registers. Just listen to Triana and Medina Azahara and any folk-rock English composer pales against these, because Triana and Medina Azahara it's the American progressive folk-rock from the 60s/70s mixed with Flamenco, and Flamenco itself it's a remix of music genres from several backgrounds. So the amount of feelings spoken and written in lyrics from that really complex tunes (from Triana more than Mediana Azahara) can't be subpar at all.