Category 0: Mechs that are actually in a pretty good spot. Let's start out positively.
Mechs that have a unique play style, not overpowered but sufficiently quirked to be somehow viable and fun to play in niche roles. Some of them could use armor instead of structure quirks, but that mostly has to do with that the current quirks to compensate clan XL doesn't really cut it across the line.
Mechs in this category: AS9-S, AS9-D-DDC, AS9-BH, AWS-9M, AWS-8R, AWS-8Q, VTR-ALL, BLR-2C, STK-ALL, DRG-1C, DRG-FANG, DRG-1N, QKD-5K, CTF-ALL, CDA-ALL, BJ-A, BJ-1DC, BJ-3, CN9-AH, CN9-Wang, HBK-4G, HBK-4P, HBK-4J, HBK-4SP, ENF-5P, ENF-4R, TBT-ALL, GRF-2N, GRF-E, GRF-3M, KTO-ALL, SHD-2H, SHD-2D2, SHD-2K, WVR-6K, WVR-6R, LCT-PB, LCT-3E, LCT-1V, COM-2D, COM-DK, SDR-5D, SDR-5K, UM-ALL, JR7-O, WLF-ALL.
I am not saying they are competitive or anything, but IMO it would not be very productive to give them stronger quirks, they have sort of reached the limit. You can have a fun game in any of these under the right circumstances. (OK, give VTRs JJ buffs!)
Category 1. Mechs that were inflated by the rescale and/or received other durability nerfs
These are mechs that either lost armor quirks for structure, or that had their structure quirks nerfed in the May-Jul patches. To make it worse, the meta has now shifted from Lasers to PPFLD damage, something that hurts these mechs even more because many of them were good at spreading DOTs by having large XL engines, good humanoid hitboxes with shielding arms. Now they take it all in the ST instead.
Mechs in this category: BNC-ALL, ZEU-ALL, BLK-ALL-KNT, GHR-ALL, WHM-ALL, TDR-ALL, CPLT-ALL, FS9-ALL, JR7-ALL
Solution: All these were in a good spot before but now lag behind on durability due to the reasons above. Give them a little bit more structure or armor. In some cases, BNC-3E/3S they need agility to help being mostly stuck with STD engines. In the case of ZEU, these used to be unique in their durability, an opportunity lost not to give them armor quirks back. The TDR-T is a good exanple of a mech that lost range quirks and was never compensated with anything else. It also used to be the only one with structure, but now most IS mechs have structure...
Category 2: Mechs that gradually lost offense quirks
Here I am thinking of several chassi that were repeatedly nerfed, especially in the big dequirkening where all range quirks above 10% were simply removed and often replaced by nothing. These were all once great but have fallen behind because of these nerfs, and because new mechs were introduced that are better than these ever were.
Mechs in this category: BNC-3M, MAL-ALL, STK-ALL, BJ-1X, TDR-T, RVN-ALL, HBK-GI
Solution: Give them back some love just. The BNC and MALs are needed to give IS something to dance with Kodiaks. The Stalkers suffer from low engine cap. Some BJs were nerfed a few times too many, and ravens and the topdog was never compensated for lost range quirks.
Category 3: Mechs that never were good enough
Here I am thinking mechs that never got the quirks to get a taste of being good. Decent sure, but not good. Perhaps because they were once in the ancient past part of the meta, or because of the more careful policy that seemed to be adopted after the first big quirkenings.
Mechs in this category: KGC-ALL, BNC-3S, BNC-3E, MAD-non3R, RFL-ALL, CRB-ALL, SHD-GD, SHD-5M, SHD-2D, DRG-FLAME, DRG-5N, WVR-7K, WVR-7D, WVR-Q, GRF-1S, GRF-1N, HBK-4H, CN9-A, CDA-3F, JR7-nonO.
Solution: No general solution, very mixed sallad here, but KGC and CRB should be a hard nuts to crack imo, no brainer to give it armor. BNC-non3M needs agility and durability, MAD could use even more durability, Some forgotten mechs just need attention, or the correct quirks for their potential builds.
Category 4: Hopeless mechs
A very personal list, but these I feel we should just let go. If you quirk them enough to be good they become too ridiculous to exist...
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Mechs in this category: SDR-5V, CDA-3C, perhaps I'll also leave Highlanders and Orions here as far as I'm concerned, but I guess JJ's could do it for the HGN. Hmm, turned out shorter than I had expected. Lets add loyalty and hero Wolverines here too, though they could be salvaged.
So, point is, there are many mechs that need help to get back up in the saddle again. I miss the early spring last year when you had sooo many mechs to choose from. It was great fun to play back then!
Have fun!