They're actually pretty fucking bad if you want to be effective for most situations.
A certed AP MBT is a jack of all trades. You can halberd shitties and tanks, AP mans and tanks, etc. A vanguard with rank 1 shield, a halberd, an AP cannon, plus a few ranks in side armor etc, would come to be 2500ish certs. You would get most of the utility, at much less cost.
With a harasser, you require far more specialization per role.
Off the top of my head, chassis is a good 700 (mandatory), vulcan is another 1100 once you've got thermals (you really do need these to kill bailing tankers obscured by smoke - there is a significant difference), 2250 for boost (roughly), this being absolutely critical, and 330 for the cheap mineguard, as well as about 700 for fire suppression, another absolutely critical to max out slot.
That's basically 5200 certs for a cheap yet effective AV harasser. Ideally you'd run stealth as well, but that's an extra 1000 certs over mineguard.
The difference once you've used a fully certed harasser, to a stock one, is absolutely huge.
If you plan to go anti-infantry, you're also looking at a good 800 certs for a low-tier marauder, plus you either want to be running stealth, radar, or composite (composite is only worth it if maxed out) - these all being significant cert sinks over the default AV mineguard build.
Harassers take a lot of certs to get going well. "1000 for a sweet ride" barely covers the gun. You're talking a "gun + rank 1 fire supression" shittermobile. An extra 500 throws mineguard and maybe rank 1 of a chassis. Absolute shitter tier. You will die significantly more than one in a well certed vehicle would. Basically, the difference between a low tier shittermobile harasser / well certed one, is much more significant to that of a low tier shitter MBT and a well certed one,
t. TR/NC harasser autism trim haver