Sentinels suits are a minor problem compared to scouts.
All sentinels suits need is their damage profile resistences taken away, HMG tweaks, and forgegun tweaks.

Scout suits were developed totally from mainly aimless suit designing, where there were no actual solid team based roles in mind for the suits.(Best example is the assault and commando. Sentinels however are pure defense and pure offense, which are not usually good things to add in a game in the first place considering how you have no other functions than said role)

Except the scout suit obviously is exploitable in many ways compared to other suits.

If HMG's ROF was set to 1200(1200 already being a line of bullets), and they were removed of dispersion(with normal HMGs just being around 18 metres of an effective range and Assault not ever passing 24 metres), and small HMG clip size increase to complement these changes, they might not be a problem. Besides that I would remove their splash damage bonus and replace it with, say.... A slight resistence to damage taken by long ranged weaponry, and skill bonuses that increase the reload speed and clip of each sentinel suit's racial weapon sidearms(for when emergency calls)
Forgeguns, having the effective range of 400 metres, can snipe infantry and vehicles well across the map, which is ridiculous.
Ranged AV weapons really should not have any effective ranges over 200 metres(being half distance of the map is still spoil the AVer, but for forges it'd be fine and they really needed a heavy distance cut for quite a while.)
Assault forges can kill tanks before they can even run away, mainly because forge AVers use damage mods to heavily boost the forgegun's strength from suppression to being as lethal as possible, and because of the quite unnecessary idea to make ADS extremely underpowered/bare minimum hp/their speed sometimes can't make up for their lack of power, normal dropships as graceful as a whale in flight, and tanks being just barely driveable/maneuverable. I'd combat that by having very strict damage mod penalties for forges(maybe even hardcode the forges to not be affected by them) and that assault forge craved a much needed shaving off of 300-200 or so damage points.

Besides that, there is scout suits, where the vast majority of scout suit users are likely to be any other kind of unfavorable player exploiting whatever they can find(Who's driving the invincible ultra repping madrugar? A scout, Who's using a newly added map sky scraper to snipe? A scout of course. This of course will look biased but if you observe your matches you'd see it happen)
Scouts are a mess and it may be that giving them some coherent role(besides reprogramming them to be pilot suits or so) may not be probable.