There's nothing wrong with a tail emission, even if you let the normal Bitcoin supply run on as is by the time the "21 millionth coin" is minted, the outstanding supply will be drastically lower. It's been only 17 years, and 17% of Bitcoin is already lost, by 2130 most Bitcoin would be gone by then leaving little to none to circulate. That's about 1% of Bitcoin lost per year, so in 100 years all Bitcoins would be lost, ignoring Satoshis coins which are unlikely to come back in circulation. There will never be 21 Million Bitcoin exactly, no matter how you slice it.