Actually, now that I think about it, the Lieutenant XP requirements have to be lower than any tank worth taking in your platoon, which is why the LT outpaces the good tanks so completely. They are probably counting on your tanks having multiples and the resulting XP bonuses. Well, unless you're unlucky, you don't have that for many of your 5 stars, which gain XP painfully slow to begin with. But even then it's not equivalent. Case in point: my Sarah (first day 5 star, been in every battle I've done) is at level 32. My second ever 5 star, Meiling, had a dupe shortly after I got her and she's at...level 32. So it's enough to catch up, and yes, she'll eventually surpass Sarah, but it's just not as big or as prevalent as they probably seem to think it is. Meanwhile my Lieutenant is at level 43, eleven levels higher than a tank that's been in every battle since the beginning, and five levels higher than the highest level tank I have (who has an 18% XP boost).

The only tanks I have at the max 30% XP bonus are 1-3 star tanks I'd never even send out to scout, let alone fight in my platoon. (And I only do that out of stubbornness.) So I don't know if the LT gains XP at the same rate as a 1-3 star tank, but it's probably on the wikia somewhere. Ironically, it seems the only way to gain better relative XP for your tanks than for your Lieutenant is to do exactly what they said they didn't want us to do...farm Angora over and over again to boost Renee's XP gain, feed her to your platoon's tanks, then repeat until either you get sick of the process or you have your good tanks where you want them.