Ease of use
I think Playmaker wins this one. It uses a state machine approach, which is intuitive to grasp, more than scripts. It still uses the same concepts and is made of mini scripts (called actions). This also allows you to write your own in C# and transition into coding. The tradeoff is with the last point.
Tutorial and General Help
A lot of walkthroughs and tutorials exist for plenty of game genres and mechanics, on YouTube. The forum is helpful, and you can also get extra actions and templates from the Ecosystem.
Possiblity to build a game completely in Bolt/Playmaker
Depends on the game and what you mean by “completely”. In spirit of the question, I’d say generally yes. You can make the game mechanics, i.e. what gameplay scripts would normally do. Most people use several assets, for all kinds of purposes, multiplayer, audio managers, AI etc. That’s stuff you would normally not code or are also advanced in code. Playermaker works in play mode, so the whole area of editor scripting and tools etc is outside of the scope as far as I know. It’s also less ideal when you want to realize a big RPG, where you want to derive classes and manage tons of data, though there are even Playmaker solutions for this, like DataMaker, which is an addon (PM has addons, too).
Speed of Prototyping
Good, and manageable learning curve, but again, it depends. The tradeoff is this: you can make relative advanced mechanics and whole games with Playmaker, that’s very nice. I remember that I figured out a grapple mechanic fairly quickly, where I would otherwise trip over syntax for days had I tried to code it on my own — you just don’t know what is wrong, your idea, or because you made a stupid syntax mistake. But that advantage is moot when you plan to play around with very common elements where you can as well copy paste scripts, and learn to code right away. There are tons of scripts for conventional genre mechanics, so in those cases I say, skip Playmaker and script right away.