I think it's fine to start without bans as long as they are as proactive about banning as they have been with Pioneer. Giving a format a little breathing room at the start is personally something I'm a big fan of.
Those cards were all undoubtedly powerful in standard, but a wider card pool is sometimes enough to make them more balanced, so I'm in favour of giving a bit of time to see how things pan out.
I don't personally play on Arena so I'm not too up to date with how far back Historic goes and therefore how realistic the answers to these major threats are going to be. I know Arena had cards as far back as Kaladesh, but given how poorly Arena has been managed I won't assume it includes everything since then. All that said though, I think with any new format, keeping the initial ban list as empty as possible is a good thing providing they are proactive about bannings if they are needed.