False, since the GC was introduced. It's the opposite now actually. Solo is significantly more difficult than team play. The reason is that, as is well known, GC continually spawns/repositions zeds anyplace the player(s) isn't currently viewing. Well, think about it. With 6 players in the same general area, they are viewing most, probably all, of the area around them. With one player, it is unavoidable to not be viewing the 270 degree arc directly behind you. So in solo play now, mobs of zeds absolutely continuously spawn within melee striking distance behind the player's back. And if you turn to fire at them, then more mobs spawn in the new space which is now behind you on the other side, meaning you are now surrounded. Anyone who hasn't actually tried non-zerk solo play on HoE with the latest game conductor will be in for a surprise. It's really quite insane now.
As someone who was trying to train up by playing solo before playing in multi so that I wouldn't be a huge liability (I wish more people would do that, at least only once or twice to get acclimated to the controls and stuff), I can confirm that once I got fed up with solo's recent BS and jumped into multiplayer despite not hitting 15 with every perk my winrate skyrocketed, even on Suicidal (which is the highest I'm willing to go in pubs), even with the huge increase in zed number and non-trash zed health.
And it wasn't because I was being carried, either, because I'm often firmly in the middle to top of the scoreboard (unless I'm playing Berzerker because then 20-50% of the enemies get shot before I can go fight them, depending on the map) and often get the Giant Slayer accolade (especially if I'm playing Support which I personally find hilarious as it's a huge spit in the face of everyone saying Support is crap, some of which are probably even the same people who were in the room when it happened) which should be an indicator of being a credit to the team. And yet, if I play solo (as anyone but Medic or Berzerker), my winrate has plummeted due to the GC goin' nuts. I even lose on Hard sometimes, which I had worked up to an 80%+ winrate pre-GC before graduating to Suicidal training, because I go to shoot at a Scrake and I'm suddenly deluged in Crawlers, or I find myself suddenly facing two Flesh Pounds and I can't get any distance at all between myself and them because GC increased their movespeed, or I'm trying to gain some distance while reloading and I'm getting nipped at by Crawlers and Gorefasts because they can keep up with max loadout non-movespeed perks even on Hard. It's pretty absurd. Whatever TW had thought the GC would be and whatever TW had hoped the GC would do, it probably wasn't this.
You know, now that I know about the kind of absurd out-of-sight movement speed multipliers zeds get when they can't see you, I'm starting to wonder if it's actually not spawns or teleports that are getting them stupidly close to us, but if, instead, it's extra movespeed stacking multiplicatively with out-of-sight movespeed making the zeds essentially flash step right next to you. Pretty much identical to teleporting, but
not the actual teleport mechanic's fault. That might be why no one has found the problem yet, maybe we're looking in the wrong place.