For a bit more context to this tierlist; Joust is almost always decided in the first few minutes of the game*. Even the game state after the very first wave can be enough information to decide the outcome of the match.
The significant gold and xp lead you can amass by having the better waveclear + poke is enough to get a level (or more) over your opponents. Being able to win the brawl at the very first wave can snowball into your team getting red, their blue, sidecamp... you name it. Even just getting them low enough to the point where they're risking losing the next fight is already more than enough damage done.
With that context in mind: a lot of the higher ranked gods have the base damage needed to secure kills, the cc required to actually setup the kill and an amazing ultimate. Everything below (S- or lower) tends to just be a downgrade, or has a very exploitable weakness making them too easy of a target (or potentially too heavy to carry).
*From my own personal experience. While there are games that go late (20+ minutes), there just simply isn't any big comeback mechanic in Joust other than the winning team making a massive mistake. Versus teams that try to turtle you get enough room to grab all the camps on the map, and you can always go Emperor's Armor and tower dive with your level and item lead.
These should always be visible in the pre-game lobby; either because they've been banned or they've been picked! I highly advice trying to grab one of these if you're first pick (or prepare for them if you aren't).
If you manage to get one of these in your team, you should be significantly favored in the early-game.
These gods have incredibly strong setup potential for the rest of your team. The sheer amount of CC and damage these gods can output early game are why you're picking them.
Very strong gods with good kits and no crippling weaknesses. You should be more than happy to pick one of these.
Strong gods that are more than viable enough to secure a win.
Solid gods, but should primarily be picked if they are countering a god on the enemy team (for example no good escape on their mage/hunter or a unique way to disable it).
Can definitely fulfill whatever role you're trying to have them fill.
Risky picks. Only pick these if you are a god on them, or feel like they perfectly match up into their team.
Very risky picks. These gods can definitely work, but are unlikely to achieve what other gods can in the very first few minutes of the game. Luckily, albeit incredibly rarely, you do sometimes get the time to scale and recover but why would you risk it?
Either take too long to get online, or are simply just massively outclassed in what they're trying to achieve in a team. These gods are just too low-impact or too easy of a target.
Either they make the rest of the team composition too awkward to build around, are just too squishy and risky or just straight-up don't offer anything worth talking about. Don't pick them.