Yes, it certainly is subjective! I assumed direct would be better with the axe as well, but I guess its just trying things to see what appeals individually. Im just buying an interface for mics and wondered if it would be worth spending a bit extra on the Apollo
i don't think the axe running through it would be a reason to buy an apollo vs something else for mics. i'd ask what effect the apollo has on mics specifically vs other gear.
i really don't think there are night and day differences with most gear under say $1500 or even under $1000. i use a behringer xair 12 for my live streams with $1 1/4" cables and it sounds great. from there, i use a $20 RCA usb stereo interface to get it into the computer and it still sounds great. that's probably the cheapest digital mixer setup i could use.
of course, using other more expensive gear sounds a bit better, but it's not like my cheap setup is full of noise or sounds bad. i've used more expensive gear too, and yes, it's better if you compare them, but not by that much. once you get past $2000 and more, then you really start to hear significant differences, but even then, it may not be worth the extra money for a bit more low end, for example. it really comes down to the details and what you're looking for or missing.
remember that expensive gear exists for a reason. most manufacturers have low and high priced items so you buy the low priced gear to start, enjoy the company, then set a goal to someday get the high priced gear. but the high priced stuff isn't always night and day better. just be diligent knowing the differences. something like the Axe3 vs the FM3 is more clear cut because they sound identical, but the Axe3 would be for those who need more CPU power or more I/O. that's much easier to decide than the "voodoo" of higher end preamps that may or may not be better in your setup.
hard to say. gotta do the research, but ultimately in my experience, there is a range of lower-priced gear that sounds maybe 95% as good as something 3x the cost. we can spend infinite amounts of money always getting "the best" thing, and sometimes the difference isn't worth it. (it always depends on the specifics!)