always allocate investment in new coins smaller than your investments in high ranked, reputed coins like btc and ethereum, it's simply basic risk management that despite the fact that your saying is true, still 90% of altcoins could be losing their value easily.
even though it always comes back again with your capabilities of choosing best project out there.
you just couldn't always accurate in your investment so it's better to be safe than sorry, after all even coins like bitcoin and ethereum isn't lacking ROI as long as you have the sufficient capitals to invest in them.
I never like the idea of allocating some investment into new coins not to talk about an existing coin that is already doing well in the market because this current market season is also determined by the trend the Bitcoin market showcases and the last time I checked the percentage of altcoin that always losing in their value easily is 99%, not 90% because the altcoin market are always highly manipulated.
As you said, it is better to play safe and DCA in Bitcoin than waiting to have big capital.