I actually am going down this rabbit hole specifically because I came up with what I think is a rational technological justification for mechs.
The idea is basically instead of just armored walking tanks (which is what Battletech canon says), mechs have really strong forcefields that shed a lot of EM radiation that messes with remote communication and can fry any fragile transistors.
So like, a lot of the stuff we use today - cruise missiles, drones, and the potential of stuff like self-piloting computerized vehicles - don't work because the EM release of the shields will fry anything other than a pretty simple system with a lot of hardening.
The way shields would work is that they 'harden' against impacts from the outside, but normally they're uni-directionally permeable so you can launch your own missiles and fire your own ballistics. When something impacts, the shield pumps some energy into the spot hit to nullify the whole impact. However, if you get hit in rapid succession in different locations, the shield struggles to recalibrate to block them all.
Basically, multiple scattered hits bring the shield down faster than singular big hits. A big cruise missile like a 1 ton Tomahawk is less useful than peppering a mech with a half-dozen 10 kg rocket propelled grenades. This brings the range of engagement much closer than what happens with modern smart missiles.
You could also just totally obliterate a mech with a cruise missile (or a high-explosive tank shell) if you could hit, but you'd need to time it right to hit after you drop the shield but before the shield can get back up. The three main weapon types are thus:
Lasers - go through shields, but do fairly minimal damage.
Small Missiles - best at dropping shields.
High-explosives - best for killing shots.
Ok, I had a quick look to refresh my memory and mechs are huge, house size or larger in height. They can be seen from 10's of kilometres away.
This makes them vulnerable to direct artillery fire from cover to the area that they are moving in.
They weight in the same range as tanks but that load is all on the feet. I doubt that they could manoeuvre on most surfaces. The soil would not take the weight.
They are fundamentally unstable, so are humans but it is worse for a mech and they are very vulnerable to trip effects and land mines targeting the feet and ankles. This also makes for more complex maintenance and logistics.
These are my principle objections to mechs. The big one is size and it has gotten worse over time. We have drones that are hard to spot and could spot mechs moving from tens of kilometres away. Once they can establish range and movement vector, just call-in artillery from out of line of sight to the mechs and bomb the area until there are no more mechs.
I will add that if they are generating that much em from their shield then use that em as guidance or method of location.
Also, the shield has to be a complete shell or it quickly loses its stability and collapses. If you put a shield around, like, a tank, the tank treads would be spinning against the inside of the shield, but would barely transfer any force to the ground beneath. If you put a shield around a plane, the airflow would be blocked so you couldn't get lift.
But due to the way biped locomotion works, lifting the feet and then striding, you can put shields around a mech and still be able to move.
Are you saying that the mechs are effectively in a hamster ball of shielding and are stepping on that to move?
If the mech is moving by putting weight on the forward edge of the shields could not a wheeled vehicle not do something similar?
How does the mech shoot through its own shields?
Can the shields be shaped to work as a ground effect vehicle?
All that said, had wave it away and play with mechs.