So, a "feature" of FF6, even vanilla is that battle speed only affects enemies, and not you. If you set that shit to 6, you're just going to make it WAY harder on yourself to start, for no reason. 3 is normal, 1 is easier, 6 is harder. This is not fixed in T edition, though wait tricking is (Like in FFV, any time an animation is playing your ATB gauge pauses. In vanilla this is an exploit known as wait tricking where you enter wait mode ATB, play an animation, enter magic/item menu, and wait for the animation to play out so your enemy doesn't get free turns off of long ass animations). A core mechanic of it is just exploiting the shit out of enemy weaknesses, and stealing EVERYTHING. Some relics now give you access to spells, and you can get relics before you even reach south figaro for the first time.
I'm not sure what early boss you're talking about, I can only assume the Guard Leader in the narshe caves? He summons tons of dogs, and his charge can chunk the moogles down pretty fast. Or maybe the Magitek Armor around the castle? Magitek Laser hits everyone for 30 or one for like 75.
It doesn't really get easier, but enemies doing rapidfire attacks also doesn't sound right. It doesn't get to be totally bullshit with one hit kills/effects until you hit WoR (where you should have relics that negate those status effects anyway)
What version of it are you on? Older versions are definitely buggier, crash-prone, and have bullshit like the costumes (sprite overwrites) having stat bonuses which means you have to look like a stupid hobo or a KMMO player for the best shot at fighting bosses in EX. An important point to note is that T edition is a jap romhack for the jap game, with an ENG patch laid overtop, which introduced bugs all of it's own. Regardless,
here is an aggregated set of FAQs from both JP and ENG patch notes, readmes, and more, might offer some insight.