only problem with using dive is that sub/protect will destroy that, while they stat buff up on the turn you go diving... If it's really a stalling one with protect/dive/seed/one attack, then you can keep switching (if there's no spike) to fend off the seed, making 3 of its move useless. Sub can easily block leech seed as well... The greatest thing regarding Ludicolo is that poison/flying weakness, which is STAB on 2 fast and scary Pokemon: Crobat and Aerodactyl.
I don't know... Ludicolo with rain dish is not as strong as when I first started playing... I trace most of them with Porygon2, and I get swift swim most of the time. Substitute is really an easy way to destroy a Ludicolo... it messes up the setup too badly, which severely nerfs Ludicolo into a weaker version of Milotic.
To me, Milotic > Ludicolo... lesser weakness, and marvel scale to make it extra annoying. Recover heals a lot more than leech seed can... so yeah, definitely more annoying.