I totally saw this wall of text coming the minute I posted.
I think it isn't fair to say "unless there is a good jungler present", because that is a big part of the game. Top is probably going to lose anyways if the jungler is bad. Some tops need less jungler involvement and have more natural sustain. And I'm not debating Jayce's power, but how he compares to other champions of his role.
Well comparing Jayce to other champions would've been an even bigger wall of text ;p
WARNING THE NEXT PARAGRAPH IS MY PERSONAL OPINION AND SHOULD BE TAKEN WITH A GRAIN OF SALT
I can understand why Jax (or mr.permabannned malph/shen) would be a better pick than Jayce in almost every way - I see little reason to pick Irelia/Yorick/Darius/Teemo/etc. over Jayce in most cases - yes I'd want Irelia if I play against a high armor comp (taric/shyv/jarvan or smthing), yes I'd want Darius if we're running an early game invading comp (with nunu and stuff), yes I'd pick AP nid top if we have a Xerath mid and an Ezreal bot, but if I'm looking for a general pick Jayce is my go to guy - simply because he can win his lane consistently and still have ok to good scaling into teamfights.
Look, fine, it's your opinion, I'm just saying try it a couple of times, if it doesn't fit you, cool - difference of opinion, and that's what makes LoL so great and frustrating at the same time.
btw i agree with you on the jungler - if you got a bad jungler and they got one that loves top and ganks it well, you're going to have a bad time no matter which champ you play - but look at it this way, if their jungler is forced to come top, then that opens up many things - such as counterjungling, bot ganks into dragons, and less pressure on other lanes
btw stranglove, I love the bomb and out of those five champions, I've never met a malph top lane in the 30 or so games I have with Jayce (he's perma ban and all), I've won lane against the two teemos (the trick is a pink ward in lane and then harass with a Q + autoattack + E melee combo, and kill him with the next one while avoiding/destroying the shrooms), yorick is always the same lane - either rush a bloodthrister/wriggles or get an early gank (out of the three yoricks i faced, two were just farm lanes where i was behind by ~20 cs by min 10, and then I stayed at 20 cs behind until min 20, the other one my jungler carried my lane), kayle crushed me the one time I played against her, and Cho i've never faced - but I'd assume you simply have to dodge the rupture and you're golden (his large HP pool is useless against your E in melee form)
Simple, he has a bad pre lvl 7-9, but he can still farm well enough in those levels because he has a ranged auto attack along with above average escapes.
Once you max out his E, you'll do 25-35% of the enemy's HP in a single hit from his E in melee form on a low cooldown of 10 seconds. Three or four hits from that ability alone WILL kill you. This is ignoring the fact that he still has the proc from switching to melee form, and his Q and autoattack damage, and the fact he'll knock you back at the same time, making response difficult.
He's hard to itemize against in lane - his E in melee form does MAGICAL damage (based on your max health too). The rest of his abilities do physical damage (don't forget he's capable of doing physical in ranged attacks). HP/Armor/MR are all bad choices - sustain is your best bet, but his damage will always outdo sustain from items.
Bottom of the line, you'll never win a lane against Jayce without good jungler pressure, or you simply being much better than the Jayce.
Outside of lane, if you build frozen mallet before min 20, and bloodthrister before min 35 (2 dorans, boots 2, and hexdrinker situational), you'll be set for your teamfights, as you'll be able to speed up your team, do a good chunk of damage on anyone with your E + ok scaling on the rest of your abilities, along with a free reverie for your team, as well as decent tankiness with your bonus armor/mr from melee form. (great synergy with Skarner btw)
I'll be willing to upload a couple of replays, or play with/agaisnt you (I'm on EUW, alias Revolving) - or I believe sOAZ played Jayce quite a few times in the recent tournaments - and I heard he was successful - although I did not see it for myself.
TLDR: Jayce outscales all other top laners with levels in lane - and is able to contribute in teamfights with decent to great damage (depending on how far your item build is), speed up (GREAT for catching people or getting a better position), and slows (mallet + Q in melee), and a knockback.
If you like skillshots, try Lux. High early-mid game burst potential, good poke late game. Very fun if you get her down - frustrating if you keep getting caught.
Ziggs is a high skillcap champ that has a great early-mid game as well - can potentially win almost every lane if played well.