I haven't had major issues with this, but that's because I only play warden on maps that support it - in other words, that have spawns that aren't too easy to camp out. You have to play smart what maps you go warden on, or yes, you will get camped. I also usually do not play warden for an entire map, because once the enemy team catches on it's much less effective. IMO getting insta-gibbed is the risk of going mole - that's why you have a free respawn as your ultimate.

Changing the mole time changes the ability drastically. If you spawn before freezetime expires (old school style), you get insta-shot by people who look for names colored of the opposite team - if you're really lucky and no one notices, you can tear half their team apart before getting killed. If you spawn immediately after freezetime expires, you have the same scenario as before, but with vigilant people looking out for those appearing as freezetime expires rather than name colors. If you spawn 3 seconds after freezetime, you have a hybrid which can do pretty serious damage, but also has the risk of being camped, though less so than 6 seconds (our current setting) due to the spawn rush possibly still creating confusion. Finally, you have our current setting of 6 seconds.

Of those four hypothetical settings, the first two I strongly disagree with implementing - if you go unnoticed you can level half a team's worth of heads with a silenced M4 before anyone knows what the hell just happened. I would be okay with trying out a shorter delay after freezetime to see if that reduces the likelihood of simply being insta-killed, without overpowering the mole ability.