[......]If I invested in 1 BTC, is it enough to make me a millionaire by the next bull run,
1 BTC at six digits is more likely to happen in the next bullrun but even that is already considered highly optimistic. No.
or are there an elite number of alt coins that could help me safely achieve what BTC & ETH once did?
If you mean buying one of those on top 20 using 1 BTC worth investment then there's a higher percentage that it could happen. Their market caps are still small compared to BTC so there's that hope.
Not the elite but there are many claims that people became millionaires from taking their chances on relatively new coins with maybe a thousand worth of "investment". It's up to you if you want to gamble on that.