It's potentially a bit of a trade-off. As Mr H says, worst case scenario and the flight is missed they will reaccommodate you. But that could be next day. While 1hr40 was fine pre-covid, there could be delays ex LHR with covid screening, delays on arrival with covid screening, and transfer delays for checking onward documents (for example that you meet the eligibility requirements for Australia).
Sounds like part of that is addressed by an early arrival at LHR not great for a 1100 dep but doable and hopefully by April WA will let all Australians into the State!
Will MH be flying to PER next year? They have taken a huge financial hit due to covid, have had cash injections from the State, and could look to restructure their route network.
The alternative would be longer - to take QF right through to MEL or SYD, and then connect from there to PER. Any problems with late flights and (a) there are regular flights MEL/SYD-PER rather than just one KUL-PER, (b) you are in Australia already and much easier to deal with any problems or delays.
True though a lot longer and more tedious but I'll have to think about it. Thanks for all this.