Well first of all, its impossible for a team comp to be lacking all of the above.
So if the team is missing a tank, obviously the priority would be the tank. Same with all the other roles.
If a low ELO team is lacking any role, its going to be a tank, jungler or support. Low ELO players almost always pick carries.
I find that having a tank is insignificant in low ELO. The lower the ELO, the faster the game would end (since its a race between the two team to see who has the biggest feeders). The faster the game ends, the more unlikely that team fights would happen. The lower the chance of there being a team fight, the less likely that a tank would matter.
Supports are nice in a lane. But of course, low ELO players don't realize that supports are meant to suit a more passive play style and get stupid. So its better to get a champion that can also become aggressive.
They also have no idea how to protect a support and blame you for having a bad K/D. So avoid them too.
For the two types of carries, unless your team comp is made up of supports and low damage tanks, there will always be someone that does some sort of damage. So those two are almost always irrelevant.
Missing a jungler is huge. If they have one and you don't, you're at a significant disadvantage. But of course you have to consider top being 2v1 and that solo top player might also be stupid and feed the two.
But having a good jungler is MASSIVE. Indirect carries of the game. The early game (laning phase) is almost completely swayed by the actions of the jungler.
If a fight breaks out in a lane, having a jungler in position to intervene would almost always tip it to one side.
Or say the opposing jungler is ganking a lane and your teammates in that lane is overextended and guaranteed to be dead if the jungler gets in. If your team's jungler is there to stop him before the opponent is able to gank, that just bolstered that lane significantly.
Or say you don't suspect you can pull off a gank kill since your laner is pretty hurt and the opponent isn't. Come in and hit the opponent a couple of times, evening the playing field for the lane.
Or if the laner has to go home or even died in a fight and you guys might lose a tower, you can save it just by being there.
Junglers are also the most versatile group of champions in the game. If your team is squishy and needs to be tankier, the jungler can build towards it. If your team needs more damage, the jungler can also build towards that. Not the same for almost all the other roles.
If you need to fill any role, you should prioritize the jungler first. They are the determinants of the early game, which is absolutely huge.