It's still profitable to invest in alts regardless of how far the market has gone but you have to be very selective about which alts to buy since there are so many and most of these alts are at their alk time high prices without a clear cutout path of where its heading next.  I would suggest that instead of buying alts that been trending up, you should check out those that are yet to make big moves. What that means is that you should consider altcoins that aren't in the top 10 list too.
 
Lest I forget, in order not to make the same mistake in the past, I highly recommend that you take some risk management lessons so that you would strategize better if the market decides to take a dive like it did in 2018.