I was assuming the a random person who you do not tust to play well = 50percent or less wins and under 100 games.
These people cant use sheid well at all, half the time they use it when the target is going to be taking under 100 dps for the next 3 to 6 seconds and is in no danger of dieing. I takes at least 50 to 150 games (or hon or lol experence) to learn how to play oak vs good UB builds and achive a resonable resault.
And yes if you can use abities at the right time oak and erabus are harder to kill than sedna but that does not make here squishy, everyone else definately dies easyer. Sedna is pretty shitty in the current meta game but that because her dps is verry low rather than her being an easy target to kill, she is currently still the best tank up untill artifact damage it just she does not deal much damage or have any slows to chase with. Unless you are forced to start healing right at the end of the cooldown only UB (instant stun) can intentionally stun a heal with any kind of reliblity. And healing wind, priests can tank anything apart from UB, heal is just needed to remove debuffs, unless you are chosing not to buy amour and using heal to compensate for this, then things can definatly go wrong all of a sudden (this does not make sedna squishy just the player read the game poorly, i do this a lot when i pickup sedna as a one off).