Sett and Morekaiser are the ones i really miss in the guide. Especially Morde is pain to play against. Maybe i dont see the obvious strat here, but would really appreciate an update.

Well, I keep them for the sake of nostalgia. The guide's about six years old and some parts of it I like to keep as mementos of old times. ^^

I start normal D Shield and Pot. I take TP because i tend to make mistakes vs teeme especially of he is agressive with PTA for example. If he is a standard teemo i try to check if what lvl of good he is. a good teemo will never use his blind on you unless you try to farm with your Q or on canon minions.
Let him push, farm under tower make him vulnerable to ganks pre 6, call your jng on it he will love to smash teemos face pre 6.
Swift Boots can be good for chasing him down but you should build a second slow item to chase him down if the teemo player gives you the oportunity to do so.
If you farm under tower and he pressures you lure him into tower range. Bad teemos may take a shot or two. a low health themo is vulnerable to slow+flash+q+ult combos.
Try to bait his blind under tower.

Allright Bucksack, there is no clear answer to your question. I have been told Garen is useless by teammates and enemies alike, and I had to indeed carry many times. I would recommend you tried to follow my streams as I can provide good answers to all your questions there live as I play Garen in diamond 4 elo, where he's actually very hard to play and thus I can provide you with information you wouldn't get in your own elo. That being said, one general tip I can provide is the following: you'll be good when you can ignore your teammates and win the game alone. Garen rarely wins the game alone in high elo, but up to Platinum 3 it's entirely possible to solocarry super hard with him.
That's what my guide's name is all about after all.
So you need to focus less on what your teammates think, less about what they say and less about how much they feed. Your team is bad? Split toplane, force two people up there and maybe die to them, while your team is securing an objective. You can force pressure on an area of the map if you win lane, making your team suffer less enemy pressure. There's alot to say, the point here is that you need to learn how to solocarry the game while you're in low elo, then you'll eventually get better teammates on average. That being said, people feed and suck in all elos, even in diamond 4 you'll see my midlaner go 0/7 or my adc dying 11 times :')
The point is: I hear you complain alot about your teammates and their attitudes, with very little analysis of what you potentially do wrong, focus more on yourself and your own improvement and I promise you'll carry more games and get elo! :D