The reasons you're arguing against low levels in HoE are incorrect. You're saying with the damage bonuses they lack and since they increase specimen number/health, and since they have no trader discounts or starting weapon, they're ineffective, completely useless, and you shouldn't help them out with money or heals so they leave when they die after you've ensured their ineffectiveness.
Those facts may be true but you're wrong about them being the reason low levels can be useless in HoE.
They're useless for the same reason there are useless level 6's. Because they suck. At aiming, at specimen prioritizing, where to be, what to shoot and what not to shoot. This is what people complain about when that 'level 2 noob' joins and ruins their game. This is why this guide exists. It's never 'oh if that guy had 50% shotgun damage increase instead of 40% we would have been just fine and dandy'
The only thing the level 0-4 might be an indicator of is inexperience. That is the real killer. That is why they don't know what doors to weld, not to rage the fleshpound, join as level 1 demo instead of their level 1 sharp on wave 2, when and where to run, don't know map layout, or stand just a little too far forward etc etc.
As someone who's just started leveling a new account exclusively on HoE (and occasionally sui) servers, I can assure you that
a low level can easily carry a full team of level 6's through a HoE game, and even the pat fight, and most of the time I'm not pulling miraculous clutches or anything like that. I'm just camping/kiting with the team like I would as a level 6. This, if anything, shows that it's not the perk bonuses that make the player.
If you want proof, just ask for it. I'll record my next few games and post a link to a myriad of screenshots, or whatever, the point I'm trying to make is that it's people who suck that are ruining your game not their perk level - the perk level bonuses don't matter enough to be the direct cause of wipes.
People complain about low levels because they don't know what they're talking about themselves. Seriously. There's just as many level 6's who do nooby things. It's just they get called 'noob' instead of that 'level 6 noob' as a level 3 would.
Yes, it is more likely that someone with a low level is inexperienced than someone with a higher level, but it doesn't always work out that way, and I'd say most of the people who join a hell on earth game are doing it on purpose - they know what they're getting into. You're still better off giving a player money/weapons when necessary regardless of perk level, making sure they're somewhat kitted out, rather than neglecting them because you want them to die and leave. You don't have to give them the moon. Enough for some basic weapons or if you're support (6) and they're support (4) maybe throw them a shotty and use the dosh you would have given to rebuy your own - just use your head about it, and that really only applies if they've joined in the middle of a match.
There's enough money for them to kit themselves out throughout the waves if they are there from the beginning. Low levels don't absolutely need to be supported by other players. Yes, they will need money if they want that aa12 or crossbow by wave 3, or showed up on wave 9 (which is often complained about regardless of perk level) but it's not necessary. There is enough to buy what you
need as a low level if you play your part during the waves. Sure if you gave them that extra grand they could, for example, get that SCAR instead of rolling with m4/ak, but you don't have to. Unless you think your team would be better off if you did help them.
If you're arguing that they're power leveling, I still don't see your angle or why it's a bad thing. They are taking
advantage of the fact there are more specimens with higher hp. Having multiple level 6's for protection? They'd have that if they were level 6 as well anyway. That's a dumb point. If they're truly power leveling they'll be pulling their weight and that 'protection' isn't even necessary most of the time. I'll admit, I'm sometimes guilty of power leveling myself, so go ahead and tell me I wasn't pulling my weight, and was hindering the team with my selfishness.
If there are people who are truly deserving of being neglected they are the ones who neglect the rest of the team during the waves, don't respond to constructive criticism, repeatedly die because of this, or hinder the team while ignoring advice. This has nothing to do with their perk level.
Being a better player means helping your team when and however you can. This guide has plenty of tips and tactics that will help players with this, but alienating a team mate only because of their perk level isn't good advice.
Skill > Perk Level.
Just use your head when giving out money.