Hey Cameron,
this has been a topic here frequently.
The short answer is, the Makita is a hand trim router for short-duration, hand-held usage, as often stated in this forum, e.g. here and here. The bits that are sold by the manufacturer do not exceed 1/2″ but you will find that nonetheless many in this forum use bits of up to 1 1/2″ to surface the wasteboard, simply because they have no other milling motor and don’t want to wait this to be done with a 1/4″ or 1/2″ bit, and it works because surfacing is removal of only shallow depth, but using bits larger than 1/2″ is nothing that is good for such a hand trim router if you do it more frequently. The Makita hand trim router is a so-called carbon-brush, commutated series-wound motor, also called universal motor, whose speed, unlike the speed of a spindle on a VFD, is dependent on load (slows down under load), and the larger the bit diameter, the higher the load and the higher the current, and this at a lowering speed. It has been stated more that once here that when you burn up your makita, it’s usually while using a large diameter bit.
Milling pockets is usually not done with large diameter bits, as discussed here. Usually you do this with 1/4" or 6 mm – 8 mm end mills at high speed (24,000 rpm). I think this video (english version of video here) which tells which bits and which speed they used is able to give you an idea of what to use when milling pockets into wood.
If you’ve done surfacing with a 1 1/4″ bit, what do you expect from another bit?
Welcome to the forum!
EDIT: Updated to provide the link to the video in english