The thing is that the online voting is the BEST solution for JESC to come up with a public vote.
Countries such as Albania already struggle to provide a televoting result in real Eurovision. JESC is way less popular and I'm pretty sure that apart from friends, family and maybe some die-hardcore Eurovision fans, no one would pay actual money to vote for kids.
Being "forced" to vote for 3 to 5 countries is a great way to prevent that "Voting for your own country" has too much impact.
Poland ended up #7 and Malta #2 in 2017 in the online voting.
Can we just agree that Poland had a VERY good song in the first place which deserved to win? - The live performance might not have been that great but the song itself was the most modern and most accessible one. It had mass appeal. It's radio-friendly, well-produced, catchy, fun, interesting but not artsy-fartsy.
Also, let's not pretend that #2 in the jury votes didn't happen. We had adults and kids voting. It was a well-deserved win.
It's not our problem that other entries tried too much to be vocally impressive, musical-esque or whatever. In Eurovision, the most accessible songs usually can win as well, see Norway 2009, Germany 2010, Azerbaijan 2011, Sweden 2012, Denmark 2013, Sweden 2015, Israel 2018.... and if a quality entry like Ukraine 2016 or Portugal 2017 wins, everyone seems to complain about it as well.