Honestly even though Jacob's strength isnt anything exceptional, it's not as bad as a lot of people make him out to be. Lucy was able to tank Jacob's attacks because she is a tank, like every other good guy including Elfman & Lisanna(tanking Azir's attacks), Levy(tanked Bradman's), Base Sting(tanked Larcade's). When fighting multiple opponents its expected that the damage you deal is spread out among them, when it was just Lucy fighting Jacob she needed Natsu to save her 2 seconds into the fight.
Elfman and Lisanna are perfect counters to Ajeels sand attacks (in combination). Even still they are getting casually overwhelmed by him. Bradmans attacks are more abstract, so its hard to quantify them (aside from the helix explosion, which is shit). Larcades attacks are also completely abstract, they do not do direct damage, Sting did not tank them so much as simply being literally the perfect counter to them. Larcades magic has shown to be effective against characters at Gildarts and Laxus level (Human Irene as well, though at this point I peg her below those two w/o DF).
Jacob has the absolute
worst offensive attacks of all the spriggan. Even Neinharts nukes/wind magic is easily stronger then anything Jacob has to offer offensively and I rate historia much more then I do stealth which is why I have Jacob as the absolute weakest spriggan.
Both of the conditions you mentioned for Transports greatness are easily created by Stealth. Even if the opponent knows what Jacob's abilities are, which in a normal situation is incredibly unlikely, there really isnt much you can do about it unless you have the AoE AND the offensive power to oneshot him no matter where he is hiding, and the only spriggans i can see doing that are God Serena and Wahl(Sands of Death could oneshot too imo, but its even slower than Transport)
Prevents him from being attacked while using Transport, sure, but it doesn't make the AoE any larger or any harder for the opponent to jump out of the big house level AoE. And no, Jacob can makes objects invisible, there is no proof that he can make magic invisible.
Invel just with CQC and Stealth alone.
No. Invel should have a couple of ways of detecting Jacob. The first one is by making the atmosphere cold he might be able to detect where Jacob where there is lack of cold (in comparison to everywhere else). Making it snow should and identifying via foot prints should also be a viable option. Not to mention, Jacob has no way to get through the armour.
What counter does Jacob have to Sand pit, Sand Tsunami or Sand World?