There are lots of tweaks that are at least as serious as Guile’s in SF4.
Boxer’s tweaks make him more of a footsie zoning character who has an easier time playing defense than offense. Blanka is a runaway character. Chun Li has lots of changes from her previous incarnations while maintaining many of the same general goals. Dhalsim’s teleport is very different, his drills and mummy are worse, his ultra is totally new, yoga tower is totally new, he does less damage and stun than before, his antiairs are worse, and he has a real combo. Honda’s slaps don’t move him forward, his headbutt isn’t a real antiair and is unsafe against many characters, and his normals are very all different. Fei’s rekkas do much less damage and more unsafe than they were in ST. Ken has new normals, his fireball is worse, his dragon punches are probably worse, and his throw is worse. Dictator is a complete 180 from how he was in ST; in ST he was an offensive machine that could kill in one combo but had no good escapes, and in SF4 he deals crappy damage but has a million escapes. Vega has worse pokes, worse wakeup options, and his roll is terrible, although he does have some good new things too. Zangief has very different normals, the green hand and lariat are totally different, and his throws are much less dangerous than they were in the SF2 games and Alpha 2. Guile has a worse flash kick, some worse normals, some better normals, and an airthrow that’s the best it’s ever been.
Many of these changes made individual moves or aspects of a character’s game worse. But you know what, for most characters that was made up for by other beneficial changes. So yeah, command grabs are much less scary in SF4 than they’ve been in previous games, but Gief makes up for it by being more damaging in combos, having better footsies, and being slightly more mobile. Dhalsim makes up for doing less damage and stun and having worse drills, mummies, and antiairs by having more range, being more mobile, getting a new way around fireballs, getting a sick ultra, and having real combos. Honda makes up for his hand slaps not moving forward by having sick and his headbutt being a crappy antiair that’s unsafe on block in many matchups by having better combos, better footsies, and better air attacks.
Guile has to overcome a worse flash kick and some worse normals. Do you guys not see that his standing fierces are great, that his airthrow is great, that he has confirmable combos starting with a low attack, that crouching fierce is still useful if not great, that flash kick is still useful if not very good, that he has situational antiairs against almost every jump in, that he has good meaty and safe jump setups, that sonic booms are still good even though they could be better? Guile depends more on mobility, setups, and spacing than before. Let’s not take him back to where he can just react with a flash kick, let’s keep buffing the things that are interesting about him in SF4.
Guile isn’t bad, he’s just a very competitive lower tier. Unfortunately Capcom didn’t give him back quite enough buffs to make up for changes in other areas. But again, that’s not a problem with the idea of tweaking, it’s just a solvable problem with the kinds of buffs he got. Again, making his walking normals faster, tweaking some other normals’ hitboxes and damage, making flash kick recover faster, and making all booms recover like jab could I think make him a good character again without making him like he’s been in other games.