I bought the PS2 launch day (own 7 now), i would never complain about the PS2 as it has the best library ever, both the PS3 and PS4 are very far from that. Nothing to do with it's online or expensive addons.
Yeah you could install any HDD i know, but you still had the buy it though. With the xbox one wasn't forced to buy mem cards, on PS2 you had to, and still need to, it's nearly impossible to save or play anything for that matter, and you needed more then one, much more then one. The multitap also had to be bought to play 4 player splitscreen, which still was a thing back then.
It did not require changing perhaps but they where included in the PS2 package, as it should. Dunno how you compare that to the og xbox as it was the first xbox ever launched. Network adaptors werent that important cause the PS2 didn't have much online, opposed to the xbox which had a broader online part.
The ability to use PS1 controllers/mem cards was part of the BC thingy, which the xbox impossibly could have since it was MS's first console.
Regarding PC online, it's by far the best, i think atleast, it's free and Steam does everything one can ever need, for steam and non-steam games. Before steam there was Xfire (and others) which were very good for the time, xfire could create lobbys and one could launch everyone to the same server, voice chat, group voice/chat, screenshots, video's, ingame browser, even profile pages with updates on who is playing what/uploaded screens etc. Thought it was a excellent program, xfire got killed off (by steam?), steam got all what xfire did and much better now imo, so i won't complain.
Xfire came along 2004/2005 somewhere, or before? Before that things weren't as great but i never had real trouble playing BF1942, Quake 3, UT99 etc online with friends.