Thanks guys for the assistance.
Have a very merry Xmas. 
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I too have this exact issue, also on 900 package and have the Tp-link EX230V. I have also purchased the Tp-link HX220 mesh unit which is recommended with this router. It gets me more range but not more wifi performance, about 150-200Mb max.
I dusted off my old BT WholeHome mesh disks and they get 400-600Mb depending on device and distance from main mesh.
I have just gone with this for now and moved most devices over to the the mesh.
My conclusion is that the EX230V router has poor wifi hardware that just isn’t capable enough.
My plan is to invest in a better router and mesh combo, but this is just fine to keep me rolling for the time being.
I think you may be right. I have added the Strong Atria mesh and the signal and speeds have greatly improved.
I was only sent the Tp link EX230V as a replacement for the Tplink HX220, which also had issues.