i was perform lot of testing in last 5yrs since ue4.21 version. regarding marketplace assets (large environment), almost none is game ready (production game ready).for those who are always ready to argue, i note that with production game ready i mean 150+ fps on rtx3060 scalability 1. it is true that any single game have different and unique need so we cant expect from templates to bee ideal for ours. asside all ups or downs you can evaluate templates according to the complexity to adapt them to your needs. its not true that yu cant make open world games with solid performance (fps). but the sad truth is that in order to get those same performances to a satisfactory level, a lot has to be done. so first you have to know that whenever you want to get something you have to give something up.forget about the wonderful kinematics ready marketplace assets. in the best case, if you have a graphic engineer at your disposal who is able to directly adapt engine source, then of course you will be able to get the best speed/look ratio. as for the rest of us, you have two the most common options. 1st you must give up of all super duper advanced visual high fidelity …, go to extreme reduction in any possible way and you get your open world but keep in mind that the graphics will probably look like games from 10 or so years ago. 2nd you can try to keep some level of visual quality, but then you have to use other tricks, practically you have to somehow organize and intersect your spaces in owg, to limit the scenes to localized zones, and display all panoramic distances in hlod. anyway on begin first download and study epic games boy and his kite template.
keep in mind that even bahk is not optimized enough to be used directly for the game either. but its god example of owg level and yu can make additional optimisation and make them so. then you will probably get a clearer idea of what you need to do and what it might look like in the end and with what performance.