You say many things in this post. Some correct, some not. I do not know Bulgarian tax rules. So far as UK goes, a person owes tax on dividends if total dividend income exceeds £2000 and at a rate depending on total income. Tax is owed on both distributed income and that income which is retained in the ETF (called excess reportable income), so there is no great difference between dividend tax owed between holding a distributing and accumulating ETF. Double taxation does occur in both VUSA and CSPX because no tax credit can be taken for the 15% tax already withheld. If you own US stocks directly then the 15% US withholding tax is deductible from UK tax.
But this is for UK. This has been discussed a lot in previous posts. Eg