Well, naxx groups that go 15/15 in a reasonable amount of time (say average under 3 hours) - can basically bring whoever they want. For every slot available there are dozens of players wanting to raid naxx.
However, to clear naxx reliably in under 3h requires most people to bring consumes. If a good chunk of the raid is cheaping out on consumes, they are doing less dps, and even worse, if there is a wipe and not enough resist pots for loath / 4h / saph - then the entire run has to be called off until another day, or someone has to run to AH and pickup more potions.
Unless someone is a god tier gamer in bis gear and for some reason doesnāt want to max consume, there is zero reason to bring anyone that isnāt consuming fully. There are just so many players that are willing to do it who will be more useful to the group. Also the good players stuck carrying these non-consuming players, will find a better naxx group if the leaders are inviting low tier players who want to save a few hundred gold at the cost of everyone elseās time.
(so you brought a couple players that didnāt consume and wiped the raid, the following week your top dps, a couple tanks, and top healers are now signed up for another naxx that isnāt going to waste their time)
Yeah melle is def more expensive if they are properly consuming. 1) because they die a lot more often and have to re-consume and 2) because thistle tea / rage pot on CD adds up, and 3) they have more consumes that stack - firewater, mongoose, giants, food buff, sharpening stone if ally, etc.
This. Anyone expecting to be taken into naxx without an AQ40 bis toon and great parses is a bit delusional, especially on a class which there are many of.
Getting into early raids is really easy, but requirements to go into naxx are quite a bit higher because people donāt want to wipe and spend hours or lose runs because someone wants to learn a new raid. There are sometimes groups that form around new people, and sometimes groups need players, but in general it takes some dedication and work to get a toon into naxx the first few times. Even more so for players with no experience in that raid or with that raid group.