I actually usually play top, not mid.
I play both positions effectively lucky enough for me though.
I'm totally up for people suggesting changes in gameplay or asking why i do what I do and I suggest you ask 'why' to everything always forever.
I for one always can debate flash as not being good on rumble, katarina, wukong and most other champs that need no flash and the only answer back to me ends up being "See you in LCS" but I'm in the military so I can't -be- in the LCS.
The reason I don't take flash on him period is that his kit has a large slow, a ghostlike boost as well as a barrier.
This is technically two summoners that escape (although weaker) in a -short- cooldown.
The 40% slow that goes up to 95% about is icing on the cake.
On top of that at level 6 and on (You mentioning six) opens up for your ultimate to allow you to get a double kill 'easily' if you play it right.
650 (+ 150% AP) + 292.5 (+ 150% AP) on the Q and R alone (yes with full duration, but you can knock few hundred down if you insist).
20 + (5 ? level) (+ 25% AP) on your auto attacks if you play it right giving at least one before you die.
70 about from each aa.
87.5 (+ 50% AP) for each harpoon (You will hit about 1 or maybe none but I generally hit one on each).
995 HP on shyvanna.
875 HP on Elise.
930 HP + 62 (+50% AP) via shield on Rumble.
Assume the style you play in will have shyvanna at about 3/4 hp so 750 or so HP will show that even flat damage without the large amounts of ap bonus you can get will allow you to actually kill her while you get attacked.
Stick in exhaust forcing shyvanna to effectively not be there for a few seconds as well as stuck in your ult and on top of that it will force her to stay on your ult.
Now you may say she jumped on you after you ulted and then I'll counteract and say she shouldn't be that close to hit you while not using dragon form at that stage of the game.
Also even if she -is- 50/50 damage, the majority of her 'real' damage in laning phase should and will be from burnout and during ganks or if she uses it like an idiot from her ult.
On top of that, if we bias this game on elise being the jungler you should be having magic resist anyway.
__
Now for the actual 'why' are you okay being camped and eventually (probably) getting killed.
I'll start off with saying, "Where is my jungler then?". I mean, if they have elise coming top 9 times, why can't my lee sin be going to dragon, mid (which is an on the way easy gank to accomplish) and bottom (which has vastly more impact than ganking top).
You being camped means they are busy all the way top giving your jungle time to be busy with free dragons, bot lane and counter jungling.
"If you get ganked a lot then you will lose 1v1!"
Not quite, you have many options.
One is sitting back and farming under tower to regain footing.
Another is to roam (not very far) and just ult mid from long range (or bot if you are mid).
Or you can just kill your enemy by using the exhaust/ignite combo still, forcing them to sit in your ult or making them flash/ult out.
If they ult out, you are doing it wrong and wasted ex/ign. You should be hitting them with (2) harpoons and -then- ulting them. Not Busting out exhaust and expecting shyv to not just get out with a short cd spell.
the 'right way' to do it will make them flash out of your ex/ign/ult combo. If that happens it's totally fine.
Why?
Your cooldowns on ex/ign are -dramatically- shorter than flash.
If you make them back or burn flash good. You'll just do it again when they have flash at halfway cool down and kill them then. This also applies to me using ex/ign on katarina to pin them in my ultimate.
Then add in the fact that they are still having trouble top against you they will beg for more ganks. Exhaust doesn't scale down negatively and ignite makes people panic often so it's considered a threat.
This will go back to my first point about forcing the enemy jungle to go all the way top allowing your bot lane to be gank free potentially and having your jungler free to roam easier.
The last part is even if you are 0/999 you will still have a HUGE aoe slow, a strong as hell rylai (or not if you don't take it for w/e reason) 90% slow on harpoons and of course the 3 second aoe slow with 6 second cooldown flamespitter.
Add on top of that the fact you can exhaust someone like shyvanna who is chasing your adc (and of course aoe slowing literally every enemy easily) and you have someone who in fact.
Wants to be camped.
Doesn't need items besides -maybe- rylais.
Is a threat 0/999 so is always viable in a fight.
Generally wins 1v1 in lane phase or at least denies the enemy of cs dramatically if played right even if camped.
My way is NOT about being 11/0/5.
My way is about shutting down not only my lane enemy but forcing the enemy jungle to waste a large amount of time.
A good game is 9/9/9. A stomp is 11/0/5.
I call it being "Hyper Aggressive".
EDIT)) Sorry if the post is long, feel free to ask for more detail in whatever you want. I love to talk about stuff that interests me like 'meta strats' or whatever.
EDIT2)) Also I should add that if someone jumps a wall against Rumble you can hit them very easily with flamespitter, harpoon and of course your ultimate.
http://www.youtube.com/watch?v=i3g9oYttpF4 for an example overall. Go to 13:05-14:10