It's only really overpowered when NPCs use it against PCs. Enemies normally die so quickly that it isn't broken and most of them don't wear armor.
As for it being worse than those other spells, that's kind of debatable. Conjure Animals isn't as good as everything thinks it is. There's basically one or two animal choices that make it good. If you listen to Mike Mearls and The Sage then the caster isn't supposed to be able to choose the animals they summon. So it isn't that good.
The bolded line above is the flaw in the argument. Basically
all the animal choices are good. A CR 1/4 Draft horse works differently than a CR 1/4 Giant Owl works differently than a CR 1/4 Constrictor Snake works differently than a CR 1/4 Wolf, but they'll all mess up the PCs pretty good if there's eight of them on top of whatever lizardfolk were already there.
Also, Sage Advice doesn't say the caster cannot choose. They say it's up to the DM, which it is. IMG for some spells that means "random tables" (Conjure Fey) or "depends on where you cast it" (Conjure Minor Elementals) or "caster gets to request specific forms" (Conjure Animals), based on the spell description. I let spellcasters request animal forms for Conjure Animals because the spell text makes it clear that these are not actual animals you're summoning, they're fey spirits shaped into animals, and it makes sense that the caster gets to influence the shaping to an extent. But it's still a good spell no matter what you get. Eight elks? Two giant bats, four axe beaks, and two large centipedes? The latter would be more hassle for the DM to run than a homogenous group but it's still over a hundred HP of meat shield. And I didn't even know until typing this paragraph that elks are pretty vicious killers in combat--50' movement plus 13 points of damage plus knockdown is
good. The main downside is that elks have have 13 HP apiece, but if your lizardfolk shaman summons eight elks on top of the six lizardfolk warriors that are already there, your CR 5 fight goes instantly from Medium to Deadly, which is a pretty good indication of the impact those elks will have. That's far, far better than imposing disadvantage and 2d8 damage per round on one PC.
If Spike Growth makes the enemy stand completely still, then it is doing its job. (For extra fun, combine Flaming Sphere and Spike Growth! Now "you just move away from the flaming sphere" isn't so simple.)