So I am currently in the fortune position where I can invest £4k into anything I want. I currently have ~£5k in the s&p500. The decision I am struggling with is...

Even though the LISA will give me £1k a year, I would also get £1k a year if I invest into the s&p500 (£5k £4k small monthly contributions will get me to 10k very soon), with the s&p500 returning averagely 10% per year, I'll be getting that £1k. Surely the ETF investment makes more sense as in the long run, I'll be able to add to it and increase that £1k annual return? I know there are risks and s&p500 not always giving back 10% per year, but it being a long term average.

I am not looking to buy a house in the near future, purely looking to set my financial situation up best for long term growth. Reddit gurus, am I missing something?