If your friends aren’t at a good level or can’t help you then it’s gonna be much harder to level up. Honestly if your offline scene is stagnant like that it’s gonna hinder you more than playing online can help you so maybe it’s time to get back online? People give online shit but there’s lots of good players amongst the bad ones with all kinds of different strategies and skill levels. It’s also pretty good for learning basic matchup knowledge.
Also people tell you to watch high level gameplay to improve but I find you need to get to a certain level to use those videos properly, yeah you can get basic combo/setup ideas but you have to look at what these players are doing and understand WHY they are doing everything they do, it’s not a case of just seeing Daigo or whoever throw a fireball and think “ok, throw fireball with Ryu” you have to see the bigger picture.
Personally I would start playing at least a little online (as long as you have a stable connection) and learn some matchups better, maybe play some better Sakura players than yourself and take notes of what you can learn by playing against them, then lab it up with high level vids and vids and tech from around the Sakura forums and just grind it out if you really want to level up, anyway playing SF4 is still about having fun in the end so make sure you’re enjoying it or there’s no point.
