Some coaches are just bad at coaching in general. Actual gameplay advice should be taken with a grain of salt. Though I do agree most good coaches will recommend easier champions like Annie, Mal'zahar, Vlad, etc. They let you focus more on actual gameplay / strategic choices rather than getting stuck in various niche mechanics that only specific champions like Leblanc, Zed, Riven, Lee Sin will have to worry about.
Annie is very good for learning just general placement, warding, and keeping track of your cooldowns / abilities. The honest truth is most annie players don't even keep E up near permanently even though it's duration is only like a second shorter than the cooldown at 40% cdr. She's got a very simplistic system of use 4 spells and then stun into ult so you don't really have to keep track of much. She also has easy csing via Q giving it's mana back on minion kills. Annie is a very good character to free up focus to work on more map awareness / where to be rather than forcing you to do ridiculous outplays.
Tf is similar to annie with the only difference being he is near 100% focused on map awareness / roaming and has more complexity when it comes to using cards at the right time (When to red card, blue card, or when yellow card is best).
They both fufill similar purposes and do offer a lot of room to learn. The problem is if your only goal is learning to be better it will be tedious and it will be boring. If the coach isn't pointing out basic mistakes, when you have the wrong focus in situations, and not putting a emphasis on awareness / thinking decisions through in the match and why what you did was wrong they are probably bad. Everything from Bronze -> Plat is all about basic gameplay mistakes and correcting them. The real in depth niche / mindgame crap doesn't really matter until Diamond / Master.
Your leblanc is perfectly fine in terms of win / loss and consistent kda. You do however have a major issue csing on leblanc. If you wish to reach plat / diamond a good goal is 6 - 8 cs per minute every game win or loss.
Also if your emphasis is truly on learning you should choose a set pool of champions that introduce you to differing play styles without being overly complicated kit wise. Anything overly complicated risks developing bad habits or gaining knowledge that is worthless if you play another champion. This set pool of champions should be spammed. Just play one in the same role until you lose or have 6 or 7 wins in a row on them and then move to the next one. Oh and don't take them into ranked until your consistently winning with them in normals.
League at low elo is all knowledge and very little mechanical. The sad fact is Bronze, Silver, Gold, and even low plat are all actually low elo. There are legitimate bronze players that have the mechanics to outplay like faker (even scripters) and still manage to lose games due to not making sound decisions (Kill focus over objectives, not pushing leads, just not using their weight in general to win). At the same time there are plat players that honestly have bronze mechanics and still manage to win because they made better decisions.
A good youtuber for you to watch would probably be LastShadow9. He consistently uploads videos of coaching sessions for all elos from bronze to Challenger and He also does lcs game analysis.