Posts in the Bug Reports forum are supposed to have evidence.
For the first issue: devs here won't do classic research most of the time. We the players are supposed to find the documentation that mobs' charms were level-capped in classic times. But I bet they weren't.
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For the second issue, that's exactly how that's supposed to work.
If a mob DOTs and Roots you, then you charm the mob, its DOT and Root will come off of you. It doesn't work the other way - you DOT and root the mob, then charm it, it's still DOTted and Rooted.
Likewise, if you DOT and root the mob, those detrimental spells will come off of the mob when it charms you. But when it DOTs and Roots you, then charms you, its DOTs and roots will not come off you.
So that works exactly the same for both PC charming NPC and NPC charming PC. Whoever charms the other guy wins.