The LGUG tracker contains shares in 473 separate companies across all sectors of the American economy - tech, aerospace, commodities, retail, manufacturing, telecoms, etc. I think it's disingenuous to claim that it lacks diversity. It is certainly tech heavy, but that's because tech companies have become the most valuable. **
Except it's market cap not equal weighted so the 473 isn't particularly relevant. I've just looked it up and the Magnificent Seven account for more than 30% of that tracker. It also lost nearly 20% in 2022 when tech stocks tanked.
Market cap weighted US and global trackers are not currently as well diversified as they were due to the extreme concentration. What might have worked well five or ten years ago doesn't at the moment.
By all means invest some in a U.S. tracker. It's a market where passives nearly always outperform actives due to the concentration of returns in recent years. But there's some great valuation opportunities elsewhere and it's as well to spread the risk and not put all of your eggs in one basket.
On that note, I was burgled the day before yesterday so it's probably a good time to stop banging the drum about building a balanced portfolio. Good luck to the OP, investing is a great way to make inflation beating returns.