The web version of whatsapp does not do calls, only messages. And when you have family/friends scattered around 3 continents, traditional PSTN calling is not an option.
About Signal: especially now that Whatsapp has adopt their encryption protocol, it is very hard for me to convince everyone else to switch to Signal, and AFAIK Signal does not do group messaging, so I would have to convince other people to switch to an inferior solution with no extra value to justify the tradeoff. If I had decent XMPP/SIP clients I could at least try to sell the extra value of having your communications outside of control of any single company.
I have many gripes with my Ubuntu phone, but this isn't one of them. Aside from my personal preference of opting out of Whatsapp, they do have the webapp version so you don't need to carry that Android around once registered.
They also have Signal, which works well. I SSH/tmux into a box with command line Finch (pidgin for CLI) and IRSSI when I really need to IM 'on the go' and I don't have their number for a message. Which is a rare situation.