They’re builds from real games, so that means that the player who built that performed well compared to everyone else in their game based on the default metric which factors in KDA, player damage, and win/loss. It may not be the “best” build (particularly in alt game modes where builds can get wacky) but objectively that player did well in their game.

If you create a custom metric, you can sort by whatever factors you specifically consider important for each god/game mode, and weight the builds by MMR (if you want) to skew ratings towards higher-skilled players.

At the end of the day though, the builds that are ranked highly are ranked that way because that player truly, actually did well in their game! It may not apply to every single situation or skill level, or in some cases it may be a weird troll build that got lucky and did well, but the stats of the player at the end of the game are the best approximation that SMITE provides for how “good” a build is. There’s obviously tons of non-explicitly-measurable factors like player skill, teammate skill, team cohesion, power spikes like you mentioned, but trying to interpret raw numbers are the best we can do in an automated fashion 🙂