I have been hearing that even major altcoins are gradually losing its value.
For long term investment purpose, no more investing in major altcoins recommended?
The possibility of altcoins becoming a profitable investment is still present but that won't be happening anything soon especially for the old projects. The new ones will have advantage over them. Bitcoin is the safest coin you can buy currently as it'll due to rise anything soon within the year or next since the halving effect will be initiated anything soon.