Quite a lot of material presented to tribunals is illegible.
There are good reasons for this. Many documents produced out in the real world are written under significant time pressure and in less than ideal circumstances. Notes written during, say, a disciplinary hearing are unlikely to be written in a clear round hand. Particularly if the meeting was tense.
On the other hand, a surprising number of ET1 and ET3’s require a magnifying glass and some time to decode.
If you have bad handwriting it is worth typing as much as possible. If this is not possible, you must just take as long as it takes to produce a legible document.
When dealing with existing documents that are particularly hard to read, the sensible approach is to produce a typed version. In most cases you should be able to agree its accuracy with the Respondent. Even if you can’t, it is worth doing. The tribunal can always check the accuracy against the original if there is a problem.