M33G is an older device and comes from factory with RouterOSv6 on it.
L009 comes with RouterOS v7. This means both devices had different OS and different test procedures done to them. Since ROSv7 has a different kernel and that the tests are different, these tables can't be directly compared.

And it's not because one has ARM it's necessarily "better"

As reference: Hex as same processor as RMB33G.
I 've used my device both with ROS6 an ROS7. It's not slower (not that I know and not in my setup).
There are even features in ROS7 (HW offloading etc) not possible before in ROS6.

But "upgrade" why ? Extra ports ? Extra processing power ?
If only processing, look at AX2, cheaper then L009 and a LOT more powerful. 5 ports instead of 3 on RBM33G.
Or AX3, a bit higher in price then L009 but even slightly better performance wise then AX2.

Extra ethernet ports can always be handled using a switch.

My view ...

AX3 I think will overeheat inside the cabinet, there is an exhaust fan but for noise reason it runs low rpm.

Both L009 and hAP ax3 have similar power consumption (max power consumption without attachments is 14W for L009 vs. 15W for hAP ax3) ... so they will cook similarly inside your cabinet.

I would like to understand if the L009 offers an overall better performance than RBM33G

According to official test results they should perform almost equally well. They might perform differently, but only testing in a particular setup would tell if one of them is signifficantly faster than the other one.

If you don't care about WiFi at all (because it has 2GHz only), sure. But if you want not only equal performance + ARM packages, but also better performance, consider RB4011/RB5011

If you don't care about WiFi at all (because it has 2GHz only), sure. But if you want not only equal performance + ARM packages, but also better performance, consider RB4011/RB5011

But he wants a USB port, the next step is more likely to be a RB5009, isn't it?
Same list price of 219$ of the 4011, anyway almost double that of a L009 at 119$.

Since you mention USB, the L0009 be the winner since it has USB 3.0. While RBM33G is USB 2.0. I'd go with the L009 just on the fact plus @normis's point the L009 has been more heavily tested with V7.

Whether L009 or RMB33G is better/worse is likely pretty close and depend on the exact configuration. If you have 1GB+ WAN (and generally using it to limits) and/or if running things like ZeroTier, WG, etc. then RB5009 be a safer bet.

Since you mention USB, the L0009 be the winner since it has USB 3.0.

But beware of probable interference to 2.4GHz WiFi caused by USB3 (search the internet).