Packet buffers get a bit complicated but the hand wavy explanation is you want enough buffer to be able to smooth over situations like mixed speed goes-intos and goes-outtas or jitter from small bursty streams but not too much buffer you end up delaying bandwidth/loss discovery algorithms or holding onto packets already considered stale more than you are actually helping. In the end for local switching you generally want a very small buffer but not necessarily just the smallest buffer you can find.

There are endless rabbit holes of details though. You want a buffer with at least 1 hardware queue per network queue (in advanced situations you may even want a hardware queue set per flow) and you want these queues to be intelligent - priority queues, weighted round robin queues, best effort queues. In each of these queues you also probably want things like WRED which counterintuitively helps avoid congestion by starting to drop packets _before_ the buffer is full. You also want the buffer to be as "flat" among interfaces as possible, e.g. if the switch has 12 interfaces it's best it's all 1 line rate ASIC with 1 shared buffer not an 8 port + 4 port with interconnect and it's own set of internal QoS. For non local things latency also starts to become as big a factor in buffer sizes as interface speeds.

I forget what I ended up finding the buffer size of my MikroTik switch to be but I remember thinking it should have been 4x-8x the size - whatever it was it was truly tiny and didn't seem to be operating well.

As for why MikroTik makes things with known too small buffers... it's cheaper than proper high speed interfaces but more performant than just using low speed interfaces. Sure, it's not a perfect 2.5 Gbps solid but for the price it'd take for them to do that "right" they would be able to do 10 Gbps ports "wrong" instead. I still use my MikroTiks though I just make sure not to mix interface speeds or if I do it's with something on the side where I don't really care about having perfect performance to it just a generally fast connection when I do use it.