We just don't really know. Frontier has very subtly hinted that there will be more stuff to do with the Thargoids in Odyssey or in the future, and awhile ago there was a unconfirmed leak that suggested that there was going to be on-foot Thargoid combat as Frontier had supposedly rendered models of the Thargoids themselves, so if this is true and it's something that is going to be in Odyssey then it's possible that we may see on-foot Thargoid combat and according to the lore as you may know, the Thargoids themselves were quite formidable in ground combat.
That being said, the Thargoids were more dangerous back in the day. Back in 3304 they made multiple incurions into the bubble and they attacked dozens of Federal and Imperial fleets and capital ships, along with civilian shipping, megaships and starports. However the Thargoids are never always on the offensive and they will often withdraw and take multiple months worth of a hiatus probably to regroup and recollect their forces and prepare for another offensive with a new strategy. However in the 3305's they stopped being the aggressor to a degree and started attacking starports only as a reaction to humanity's provaction, which is why when we entered and colonized the coal sack nebulalast year they went ape shit and attacked starports both there and in the witch head nebulas because both of those regions are they're space that we're invading.
I also believe that Frontier did try to experiment with capital ships being used in Thargoid combat, cause back in the good ole' 2.4 update days when the Thargoids were first released capital ships would move about on their own and they were no longer static objects, however they were very glitchy and I shit you not some of them would crash into planet surfaces as a result:
https://i.imgur.com/uMPti0I.png
