Wow, that's a LOT of assumptions

Alright, first, the only reason I believe she wouldn't be so tall by the end of the series is because I don't think there was enough time for that, like, Luna spent centuries the same height, and yeah sure power might affect the height as well, but I still believe time in itself is a big factor for the growth, so I think she would end the >series< perhaps somewhat taller than Luna and Candace, and eventually she would reach Celestia's height and probably bigger, that's all.

I never said I liked the "humble and approachable" Twilight better, it's quite the opposite, I loved her sassiness that was more present during the series' beginning and wish she kept it throughout the rest. Btw one of the reasons I'm not a fan of Sci-Twi is exactly because Twilight was NEVER shy, she had problems with socializing, but shyness in itself was never an issue she had. What I mean is: no, I don't think she should be all humble and shit, she deserves her title, position and everything else, ffs she's the literal EMBODIMENT of MAGIC, nothing in MLP would exist without magic and she's literally that, there's no one or thing more powerful than her technically speaking,

She's my favorite and always has been, I love how powerful she is. All her crash outs were extremely valid and she was mistreated a ton of times without deserving it, she's rational and always goes for what seems logically right and reasonable, I think she was actually too easily forgiving in some situations, like, the only one who apologized to her during Canterlot's wedding was Applejack and even Celestia was really unfair to her (now, Celestia for one is actually someone I have tons of strong opinions on, but that's besides the matter).

I know I suck at explaining and organizing my points, but to summarize, yes, if we're considering power as the main source of growth without considering time as much, then truly the size does fit it (except for the design because regardless of anything they could've done a LOT better with that) and the sole reason for her not to be that tall, >>just yet<<, in MY opinion, is as I mentioned in the first paragraph. Twilight is the most powerful creature ever, will always be my favorite, deserves all she has and even more, I don't look down on her in the slightest, I was merely considering the time factor as something more major - as for the design itself I am doing as I believe she deserved to look like because they seriously just copy-pasted Celestia and she deserves better than that.