I just acquired some medium pulse lasers, they do 30 Damage at 2 tons and 16 heat with apparently +1 accuracy?

My "normal" medium lasers I used before are ++ models, that do 35 damage at 1 ton and 12 Heat and +++ models with +3 to accuracy and +50% Crit.

So where is the use for those "lostech" pulse lasers? Do i miss an aspect? Are they really this underwhelming?

In the tabletop BattleTech game Medium Pulse Lasers are not particularly worth it.
They are more accurate than Medium Lasers, but shorter ranged which basically balances out.
They do more damage for more heat, which doesn't quite balance.
They weigh 2 tons which ruins the balane completely.

In this game ++ and +++ weapons totally outclass LosTech.

I never played the tabletop, just PC-Games. I had expected lostech to be like ++++ versions of weapons.
Some ultimate option that exeeds the performance of less rare weapons, that can be found on the battlefield or in stores.

In the Tabletop, Pulse Lasers are best used to mitigate movement modifiers. The TR-1 Wraith is a perfect example of Pulse Lasers used correctly. The 'Mech is incredibly fast with a long jump distance. So, it can bounce around the field like a deranged piece of flubber and not be at a terrible disadvantage with it's movement penalties.

Unfortunately, with all the liberties the computer game has taken with the source material, most LosTech is . . . mediocre at best.