It's nothing like saying nobody can survie kunai spam. I recall Madara saying something like these eyes can see through clone techniques, Nagato has those eyes. Why wouldn't Nagato simply destroy the forest so Hashirama has nowhere to hide?
Nagato has never been easily caught off gaurd on top of being one of the best sensors he's got linked vision and has shown good reaction feats, he easily caught Bee mid air when he was simultaneously soul ripping Naruto, you're underrating Nagato in this catagory. Nagato's mobility was lost from Hanzo's attack not the mazo.
Melting into his surroundings isn't an issue, Nagato is a sensor, he can see chakra with his rinnengan on top of his linked vision. He's not getting taken out by a spear which he can block against with assura path, shinra tensei or petra path.
Madara said that only he could see through Hashiramas Mokuton Bunshins with his EMS and do it now as well. Nagato however was never able to see through Bunshins and so fell for Kakashis Raiton Bunshin.
Nagato still wouldn't have mobility as he will stick at Gedo Mazo with its Chakra receivers, he will out all of his powers in the soul removal dragon.
Asura Path will not prevent Nagato from being crushed; those tendrils easily crushed Oonokis defensive golem and Asura Path isn't known for extraordinary defensive feats. Preta-Path will not absorb the tendrils, too, as they neither consist out of Chakra nor imbued with, the databook clearly describes that the Mokuton creates real trees on the basis of Hashiramas cells, the trees chakra source only exists in the ground, where it is converted into a source of life and from where Hashirama is actually controlling all trees. And here you go with Shinra Tenseis cooldown; the first spear is countered by a Shinra Tensei, the secound Mokuton will crush him like it crushed Oonokis golem, as Nagato is unable to move due to the usage of Gedo Mazo. He wouldn't even be able to survive it with full mobility, as the Shinra Tenseis interval completely restricts Deva-Path.
Fighting, for example, 10 Mokuton Bunshin that have a humans durability and can use the originals abilities, in a field Hashirama has covered with trees he can control, his shared vision will become useless, he will be overwhelmed by the sheer number.
It's may also an interesting information, that Shodai is a sensor, too. The fact that Zetsu, who is a
low quality copy of Hashirama and used only techniques Hashirama is also known to use, is a sensor, too, confirms Hashirama to be one, too.
How Nagato is going to fight Hashirama?
Hashirama can cover the entry landscape with trees and control them, he can create a group of Mokuton Bunshins with the durability of a human and the originals abilities, he can use the bringer of darkness to blind Nagato, even to blind the summons, if he didn't already crush them. Nagatos summons are trash, Sakura killed one with one punch, Jiraiya killed two with his hair and the bird with his Katon technique, the Mokuton will easily annihilate them.
The ability of Obito to spamm wood spears through Juubis arms can also be used by Hashirama. Of course, the size of those spears will not be human sized, but even if he will spamm suchlike from the size of Hakus Senbon, Nagato could not continuously repel them, even the Hyuugas couldn't do it, the amount which is spammed is just too large and would outlast his Shinra Tensei.
I see Nagato being overwhelmed.