catalyst is the best lane sustainability item in the game. when you build roa and another catalyst, every time you level up your mana will pretty much be refilled, as well as your health (if not close to it)
as for the thornmail argument i will say that 90% of games will not require a thornmail. i see non-beefy champions building thornmail when the other team is ad heavy - this is not the way to go. if it's lategame and yi and trynd have all their items, thornmail will not save you from them. they will still melt you down, sure they might take a lot of damage but you will still be dead. the best armor items for squishies (barring guardian angel of course) are frozen heart and randuin's omen. both have team utility (if the warwick on the other team tries to dive through your team to get to you, you can slow his attacks with frozen heart, allowing your team to melt him as he does nothing. randuin's can be used as a clutch cc for when you feel overwhelmed.) and provide a lot of armor, unlike thornmail which is just 'ok i have armor so now what'
i haven't tried out nerfed vayne yet, but then again i never played release vayne, i will have a game and let you guys know what i think
as for the thornmail argument i will say that 90% of games will not require a thornmail. i see non-beefy champions building thornmail when the other team is ad heavy - this is not the way to go. if it's lategame and yi and trynd have all their items, thornmail will not save you from them. they will still melt you down, sure they might take a lot of damage but you will still be dead. the best armor items for squishies (barring guardian angel of course) are frozen heart and randuin's omen. both have team utility (if the warwick on the other team tries to dive through your team to get to you, you can slow his attacks with frozen heart, allowing your team to melt him as he does nothing. randuin's can be used as a clutch cc for when you feel overwhelmed.) and provide a lot of armor, unlike thornmail which is just 'ok i have armor so now what'
i haven't tried out nerfed vayne yet, but then again i never played release vayne, i will have a game and let you guys know what i think