DS9 pissed me off because they felt the need to turn Star Trek space combat into something more akin to Star Wars (and similar to B5) which wrecked the very premise that had been previously established. Until DS9 Starfleet was presumed relatively small. The original series it was implied that the Constitution Class ships like the Enterprise were pretty much the entirety of Starfleet and roughly analogous to modern day naval fleets. Most starship combat is similar to Balance of Terror or Wrath of Khan and shares commonalities with submarine warfare. Consider the number of times that the Enterprise was the only ship near/close-enough to Earth for something etc. The entire class of Starfleet Academy was in the hundreds of cadets, at best, enough to crew a significant fleet but only in the range of a few dozen or so. The battle at Wolf-359 was essentially EVERYTHING that Starfleet had anywhere near to the core of Federation space and it was maybe a dozen ships and a massive tragedy when they went boom.
Then in DS9 you have scenes where dozens of huge ships are casually blown to bits as if they were tissue paper. In some throwaway scenes you see multiple Galaxy Class starships (with the saucer attached no less) eviscerated in a matter of seconds in a way that made me wonder how the hell they even managed to crew the damn things. It reminded me more of WWI trench warfare where you had opposing armies encounter each other in the middle of nowhere and just turn each other into hamburger. They were trying to match B5 in terms of cool space battles with tons of shit on the screen and lost complete track of their own internal narrative in the process.
DS9 didn't expand the Federation. Your estimate of "100s" of Cadets makes no sense, even in TOS era. A Navy isn't just Aircraft Carriers or Battleships. It's destroyers, frigates, subs, etc. The Constitution or Galaxy classes were basically battleships. Yes, you don't have many battleships, but your navy isn't just battleships.
Starfleet is basically a "blue water" Navy. It would be IMPOSSIBLE to have any projection of power if you are numbering in the thousands and not 10s of thousands. Plus, Starfleet Academy always came across as something like an officer's school. O'Brien in DS9 made it clear you had your "enlisted" folks as well.
Wolf-359 was what was in the area basically. IRL, it is a red dwarf close to 8 LY from Earth, which in Star Trek distances is basically a trivial distance. I'm pretty sure the show made it clear they had to assemble what they could on short notice. The wiki says it was 40 ships at the battle. Which makes sense. To use a real life example, it would be like if there was some super ship headed towards the West Coast of the US. With barely any time, all you can muster is what is moored nearby on the West Coast, with the Hawaii fleet not able to get there in time and forget about the shit on the East Coast, Asia, etc. That would be a roughly correct analogy.
DS9 dominion war was different because Starfleet basically recalled most of their ships to consolidate them for defense/offense. Real Life example again, if the US Navy said "fuck, we need to protect the country, we're under attack", then one of your first actions is to consolidate your spreadout fleet into specific areas to defend and potentially go on the offensive when able.
I do agree the battles in Star Trek were always too "linear", though. Everyone just lines up and shoots each other like old battle formations during the Civil War/Revolutionary War.
