End Mills don't like cutting full diameter at shallow depth. It is preferable to plunge at least 1xdiameter so that cutter is well supported. Downsides of going deeper are swarf build-up and cutter pushing-off.
My strategy would be to rough slots using undersize slot drill/ripper cutter then finish with end mill.
If you only have size end mill available, you could ramp to depth over the length of the slot then back-track to the starting position at depth.
Push your feed until cutter breaks then back off a bit. The extra pressure on the cutter will help support it and the fewer cuts per slot the better.