They are not compatible in either V4 or V5, but importing them is handled differently in V5. They are not in HOSTS format. If you look at the output from a gravity rebuild (pihole -g), you will see the following:
[i] Target: https://easylist.to/easylist/easylist.txt
[✓] Status: Retrieval successful
[i] Received 33321 domains, 22804 domains invalid!
Sample of invalid domains:
- 2.0]
- (easylist.subscription@gmail.com).
- &ad.vid=$~xmlhttprequest
- &advertiserid=$domain=~bee.gl|~cpashka.ru
- -ad.jpg?
Even if some of the domains are parsed, they are likely to be imported not as intended to be used in that list. As shown below
pihole -q google.com
Match found in https://easylist.to/easylist/easylist.txt:
transparencyreport.google.com
maps.google.com
google.com.au
google.com
google.com
google.com
google.com
google.com
mail.google.com
maps.google.com
maps.google.com
google.com
mail.google.com
google.com
accounts.google.com
www.google.com
There is no reliable way to parse these lists, and using them causes problems as you have seen.