T5 Terminators as mentioned by GML brings them too close too to custodes.
A squad of terminators should feel like a squad of terminators, the subtle difference between Space Marnie terminators work in groups whereas Custodes work as a group of individuals.
The problems terminators have are (assuming the points were accurate)
Not Enough damage output.
Don't Create Command points
Few Uses for them
Could we fix these, better deep strike options, more durability (without copy-pasting other "terminators" better damage output)
Being able to fire a storm bolter within 1"
Ability to gain a +1 to armour..... somehow... maybe based on them being "in the thick of it"?
Turn 1 Deepstike
Ignoring -1 with Heavy Weapons
Ignoring -1 with Powerfist
Ignoring -1 with Thunder hammer
Not obviously all of the above... maybe some? Others?